Zoom lens and image pickup apparatus using the same

ABSTRACT

A zoom lens includes a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. At the time of zooming, distances between the lens units change, and a distance between the first lens unit and the second lens unit at a telephoto end is shorter than at a wide angle end. An aperture stop is disposed on the image side of an image-side surface of the first lens unit, and on the object side of an image-side surface of the second lens unit. The second lens unit includes two sub lens units. The object-side sub lens unit in the second lens unit includes one lens component. The following conditional expressions are satisfied.
 
3.0&lt;Δ D   12   /ER   S &lt;4.5
 
1.05&lt;| f   3   /f   UN21 |&lt;2.1

CROSS-REFERENCE TO RELATED APPLICATION

The present application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2013-114628 filed on May30, 2013; the entire contents of which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a zoom lens and an image pickupapparatus using the same.

2. Description of the Related Art

In cameras, according to an application and need, the number of pixelsis increased by making an image pickup surface area of an image pickupelement large, thereby facilitating an improvement in an image quality,and conversely, by making the image pickup surface area small,small-sizing of camera is carried out. Here, various types of opticalsystems are used in cameras, and one of these optical systems includes azoom lens. The zoom lens is also used in an interchangeable lens (lensthat is detachable from a camera main-body).

If the image pickup surface area is large, an image formed on the imagepickup surface also becomes large. In a camera in which, the imagepickup surface area is large, the zoom lens is susceptible to becomelarge. Therefore, a zoom lens for the camera with the large image pickupsurface area is sought to have both, a favorable optical performance anda favorable portability. In other words, in a zoom lens, it is soughtthat an aberration from a center of an image to a periphery has beencorrected favorably, and that the zoom lens has a small size. Both thefavorable optical performance and the favorable portability have alsobeen sought in a zoom lens for a camera with a small image pickupsurface area.

Zoom lenses fulfilling these requirements are disclosed in JapanesePatent Application Laid-open Publication Nos. 2012-133230 and2012-58406. The zoom lens in Japanese Patent Application Laid-openPublication No. 2012-133230 and the zoom lens in Japanese PatentApplication Laid-open Publication No. 2012-58406, include in order froman object side, a lens unit having a negative refractive power, a lensunit having a positive refractive power, a lens unit having a negativerefractive power, and a lens unit having a positive refractive power.The zoom lens in Japanese Patent Application Laid-open Publication No.2012-133230 and the zoom lens in Japanese Patent Application Laid-openPublication No. 2012-58406 are comparatively small-sized and have a wideangle of view at a wide angle end.

SUMMARY OF THE INVENTION

A zoom lens according to a first aspect of the present inventionincludes in order from an object side to an image side

a first lens unit having a negative refractive power,

a second lens unit having a positive refractive power, and

a third lens unit having a negative refractive power, and

at the time of zooming, distances between the lens units change, and

a distance between the first lens unit and the second lens unit at atelephoto end is shorter than a distance between the first lens unit andthe second lens unit at a wide angle end, and

an aperture stop is disposed on the image side of an image-side surfaceof the first lens unit, and on the object side of an image-side surfaceof the second lens unit, and

the second lens unit includes in order from the object side to the imageside, an object-side sub lens unit having a positive refractive powerand an image-side sub lens unit, and

the object-side sub lens unit in the second lens unit includes one lenscomponent, and

in the lens component, only two surfaces, namely, an object-side surfaceand an image-side surface, are in contact with air in an optical path,and

the following conditional expressions (1) and (2) are satisfied.3.0<ΔD ₁₂ /ER _(S)<4.5  (1)1.05<|f ₃ /f _(UN21)|<2.1  (2)

where,ΔD ₁₂ =D _(12W) −D _(12T),

D_(12W) denotes the distance between the first lens unit and the secondlens unit at the wide angle end,

D_(12T) denotes the distance between the first lens unit and the secondlens unit at the telephoto end,

both D_(12W) and D_(12T) are distances on an optical axis at the time ofinfinite object point focusing,

ER_(S) denotes the maximum radius of an opening of the aperture stop,

f₃ denotes a focal length of the third lens unit, and

f_(UN21) denotes a focal length of the object-side sub lens unit in thesecond lens unit.

A zoom lens according to a second aspect of the present inventionincludes in order from an object side to an image side

a first lens unit having a negative refractive power,

a second lens unit having a positive refractive power, and

a third lens unit having a negative refractive power, and

at the time of zooming, distances between the lens units change, and

a distance between the first lens unit and the second lens unit at atelephoto end is shorter than a distance between the first lens unit andthe second lens unit at a wide angle end, and

an aperture stop is disposed on the image side of an image-side surfaceof the first lens unit, and on the object side of an image-side surfaceof the second lens unit, and

the first lens unit includes in order from the object side to the imageside, an object-side sub lens unit and an image-side sub lens unit, and

the object-side sub lens unit in the first lens unit includes a firstnegative lens, and

the image-side sub lens unit in the first lens unit includes a secondnegative lens and a first positive lens, and

the second lens unit includes in order from the object side to the imageside, an object-side sub lens unit having a positive refractive power,and an image-side sub lens unit, and

the object-side sub lens unit in the second lens unit includes one lenscomponent, and

in the lens component, only two surfaces, namely, an object-side surfaceand an image-side surface, are in contact with air in an optical path,and

the following conditional expressions (1) and (3) are satisfied.3.0<ΔD ₁₂ /ER _(S)<4.5  (1)−0.9<SF _(2N)<1.5  (3)

where,ΔD ₁₂ =D _(12W) −D _(12T),

D_(12W) denotes the distance between the first lens unit and the secondlens unit at the wide angle end,

D_(12T) denotes the distance between the first lens unit and the secondlens unit at the telephoto end,

both D_(12W) and D_(12T) are distances on an optical axis at the time ofinfinite object point focusing,

ER_(S) denotes the maximum radius of an opening of the aperture stop,SF _(2N)=(R _(2NO) +R _(2NI))/(R _(2NO) −R _(2NI)),

R_(2NO) denotes a paraxial radius of curvature of an object-side surfaceof the second negative lens in the first lens unit, and

R_(2NI) denotes a paraxial radius of curvature of an image-side surfaceof the second negative lens in the first lens unit.

A zoom lens according to a third aspect of the present inventionincludes in order from an object side to an image side

a first lens unit having a negative refractive power,

a second lens unit having a positive refractive power, and

a third lens unit having a negative refractive power, and

at the time of zooming, distances between the lens units change, and

a distance between the first lens unit and the second lens unit at atelephoto end is shorter than a distance between the first lens unit andthe second lens unit at a wide angle end, and

an aperture stop is disposed on the image side of an image-side surfaceof the first lens unit, and on the object side of an image-side surfaceof the second lens unit, and

the following conditional expressions (4) and (5′) are satisfied.1.2<ΔD ₁₂ /IH _(MAX)<1.85  (4)1.1<|f ₃ /f _(W)|<1.9  (5′)

where,ΔD ₁₂ =D _(12W) −D _(12T),

D_(12W) denotes the distance between the first lens unit and the secondlens unit at the wide angle end,

D_(12T) denotes the distance between the first lens unit and the secondlens unit at the telephoto end,

both D_(12W) and D_(12T) are distances on an optical axis at the time ofinfinite object point focusing,

IH_(MAX) denotes the maximum image height, and denotes the maximum valuein a case in which, the maximum image height changes with zooming,

f₃ denotes a focal length of the third lens unit, and

f_(W) denotes a focal length of the overall zoom lens system at the timeof infinite object point focusing at the wide angle end.

A zoom lens according to a fourth aspect of the present inventionincludes in order from an object side to an image side

a first lens unit having a negative refractive power,

a second lens unit having a positive refractive power, and

a third lens unit having a negative refractive power, and

at the time of zooming, distances between the lens units change, and

a distance between the first lens unit and the second lens unit at atelephoto end is shorter than a distance between the first lens unit andthe second lens unit at a wide angle end, and

an aperture stop is disposed on the image side of an image-side surfaceof the first lens unit, and on the object side of an image-side surfaceof the second lens unit, and

the following conditional expressions (4) and (6) are satisfied.1.2<ΔD ₁₂ /IH _(MAX)<1.85  (4)0.43<Σ_(2G) /f ₂<0.78  (6)

where,ΔD ₁₂ =D _(12W) −D _(12T),

D_(12W) denotes the distance between the first lens unit and the secondlens unit at the wide angle end,

D_(12T) denotes the distance between the first lens unit and the secondlens unit at the telephoto end,

both D_(12W) and D_(12T) are distances on an optical axis at the time ofinfinite object point focusing,

IH_(MAX) denotes the maximum image height, and denotes the maximum valuein a case in which, the maximum image height changes with zooming,

Σ_(2G) denotes a thickness on an optical axis of the second lens unit,and

f₂ denotes a focal length of the second lens unit.

A zoom lens according to a fifth aspect of the present inventionincludes in order from an object side to an image side

a first lens unit having a negative refractive power,

a second lens unit having a positive refractive power, and

a third lens unit having a negative refractive power, and

at the time of zooming, distances between the lens units change, and

a distance between the first lens unit and the second lens unit at atelephoto end is shorter than a distance between the first lens unit andthe second lens unit at a wide angle end, and

an aperture stop is disposed on the image side of an image-side surfaceof the first lens unit, and on the object side of an image-side surfaceof the second lens unit, and

the second lens unit includes in order from the object side to the imageside, an object-side sub lens unit having a positive refractive power,and an image-side sub lens unit, and

the object-side sub lens unit in the second lens unit includes one lenscomponent, and

in the lens component, only two surfaces, namely, an object-side surfaceand an image-side surface, are in contact with air in an optical path,and

the following conditional expressions (7), (8), and (9) are satisfied.0.6<f _(UN21) /f ₂<1.8  (7)1.17<|f ₃ /f ₂|<1.95  (8)1.15<f ₂ /IH _(MAX)<1.5  (9)

where,

f_(UN21) denotes a focal length of the object-side sub lens unit in thesecond lens unit,

f₂ denotes a focal length of the second lens unit,

f₃ denotes a focal length of the third lens unit, and

IH_(MAX) denotes the maximum image height, and denotes the maximum valuein a case in which, the maximum image height changes with zooming.

A zoom lens according to a sixth aspect of the present inventionincludes in order from an object side to an image side

a first lens unit having a negative refractive power,

a second lens unit having a positive refractive power, and

a third lens unit having a negative refractive power, and

at the time of zooming, distances between the lens units change, and

a distance between the first lens unit and the second lens unit at atelephoto end is shorter than a distance between the first lens unit andthe second lens unit at a wide angle end, and

an aperture stop is disposed on the image side of an image-side surfaceof the first lens unit, and on the object side of an image-side surfaceof the second lens unit, and

the first lens unit includes in order from the object side to the imageside, an object-side sub lens unit and an image-side sub lens unit, and

the object-side sub lens unit in the first lens unit includes a firstnegative lens, and

the image-side sub lens unit in the first lens unit includes a secondnegative lens and a first positive lens, and

the second lens unit includes in order from the object side to the imageside, an object-side sub lens unit having a positive refractive power,and an image-side sub lens unit, and

the object-side sub lens unit in the second lens unit includes one lenscomponent, and

in the lens component, only two surfaces, namely, an object-side surfaceand an image-side surface, are in contact with air in an optical path,and

the image-side sub lens unit in the second lens unit includes a lenssurface having a negative refractive power and a positive lens which isdisposed on the image side of the lens surface, and

the following conditional expressions (3), (10) and (11) are satisfied.−0.9<SF _(2N)<1.5  (3)1.5<f _(UN21) /ER _(S<)3.9  (10)3<LTL _(min) /fb _(LTLmin)<13  (11)

where,SF _(2N)=(R _(2NO) +R _(2NI))/R _(2NO) −R _(2NI)),

R_(2NO) denotes a paraxial radius of curvature of an object-side surfaceof the second negative lens in the first lens unit, and

R_(2NI) denotes a paraxial radius of curvature of an image-side surfaceof the second negative lens in the first lens unit,

f_(UN21) denotes a focal length of the object-side sub lens unit in thesecond lens unit,

ER_(S) denotes the maximum radius of an opening of the aperture stop,

LTL_(min) denotes a sum of an overall length of the zoom lens at thetime of infinite object point focusing and an air-converted back focus,and is the minimum value thereof in a case in which, the overall lengthchanges with zooming, and

the overall length is a distance on an optical axis from a refractingsurface of the zoom lens nearest to the object side and a refractingsurface of the zoom lens nearest to the image side, and

fb_(LTLmin) denotes the air-converted back focus at LTL_(min).

According to a seventh aspect of the present invention, a zoom lensincludes in order from an object side to an image side

a first lens unit having a negative refractive power,

a second lens unit having a positive refractive power, and

a third lens unit having a negative refractive power, and

at the time of zooming, distances between the lens units change, and

a distance between the first lens unit and the second lens unit at atelephoto end is shorter than a distance between the first lens unit andthe second lens unit at a wide angle end, and

an aperture stop is disposed on the image side of an image-side surfaceof the first lens unit, and on the object side of an image-side surfaceof the second lens unit, and

the second lens unit includes in order from the object side to the imageside, an object-side sub lens unit having a positive refractive power,and an image-side sub lens unit, and

the object-side sub lens unit in the second lens unit includes one lenscomponent, and

in the lens component, only two surfaces, namely, an object-side surfaceand an image-side surface, are in contact with air in an optical path,and

the following conditional expressions (2) and (4) are satisfied.1.05<|f ₃ /f _(UN21)|<2.1  (2)1.2<ΔD ₁₂ /IH _(MAX)<1.85  (4)

where,

f₃ denotes a focal length of the third lens unit, and

f_(UN21) denotes a focal length of the object-side sub lens unit in thesecond lens unit,ΔD ₁₂ −D _(12W) −D _(12T),

D_(12W) denotes the distance between the first lens unit and the secondlens unit at the wide angle end,

D_(12T) denotes the distance between the first lens unit and the secondlens unit at the telephoto end,

both D_(12W) and D_(12T) are distances on an optical axis at the time ofinfinite object point focusing, and

IH_(MAX) denotes the maximum image height, and denotes the maximum valuein a case in which, the maximum image height changes with zooming.

An image pickup apparatus according to the present invention includes

a zoom lens, and

an image pickup element which has an image pickup surface, and whichconverts an image formed on the image pickup surface by the zoom lens,to an electric signal, and

the zoom lens is one of the aforementioned zoom lenses.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A, FIG. 1B, and FIG. 1C are lens cross-sectional views at the timeof infinite object point focusing of a zoom lens according to an example1 of the present invention, where, FIG. 1A shows a cross-sectional viewat a wide angle end, FIG. 1B shows a cross-sectional view in anintermediate focal length state, and FIG. 1C shows a cross-sectionalview at a telephoto end;

FIG. 2A, FIG. 2B, and FIG. 2C are lens cross-sectional views at the timeof infinite object point focusing of a zoom lens according to an example2 of the present invention, where, FIG. 2A shows a cross-sectional viewat a wide angle end, FIG. 2B shows a cross-sectional view in anintermediate focal length state, and FIG. 2C shows a cross-sectionalview at a telephoto end;

FIG. 3A, FIG. 3B, and FIG. 3C are lens cross-sectional views at the timeof infinite object point focusing of a zoom lens according to an example3 of the present invention, where, FIG. 3A shows a cross-sectional viewat a wide angle end, FIG. 3B shows a cross-sectional view in anintermediate focal length state, and FIG. 3C shows a cross-sectionalview at a telephoto end;

FIG. 4A, FIG. 4B, and FIG. 4C are lens cross-sectional views at the timeof infinite object point focusing of a zoom lens according to an example4 of the present invention, where, FIG. 4A shows a cross-sectional viewat a wide angle end, FIG. 4B shows a cross-sectional view in anintermediate focal length state, and FIG. 4C shows a cross-sectionalview at a telephoto end;

FIG. 5A, FIG. 5B, and FIG. 5C are lens cross-sectional views at the timeof infinite object point focusing of a zoom lens according to an example5 of the present invention, where, FIG. 5A shows a cross-sectional viewat a wide angle end, FIG. 5B shows a cross-sectional view in anintermediate focal length state, and FIG. 5C shows a cross-sectionalview at a telephoto end;

FIG. 6A, FIG. 6B, FIG. 6C, FIG. 6D, FIG. 6E, FIG. 6F, FIG. 6G, FIG. 6H,FIG. 6I, FIG. 6J, FIG. 6K, and FIG. 6L are aberration diagrams at thetime of infinite object point focusing of the zoom lens according to theexample 1;

FIG. 7A, FIG. 7B, FIG. 7C, FIG. 7D, FIG. 7E, FIG. 7F, FIG. 7G, FIG. 7H,FIG. 7I, FIG. 7J, FIG. 7K, and FIG. 7L are aberration diagrams at thetime of infinite object point focusing of the zoom lens according to theexample 2;

FIG. 8A, FIG. 8B, FIG. 8C, FIG. 8D, FIG. 8E, FIG. 8F, FIG. 8G, FIG. 8H,FIG. 8I, FIG. 8J, FIG. 8K, and FIG. 8L are aberration diagrams at thetime of infinite object point focusing of the zoom lens according to theexample 3;

FIG. 9A, FIG. 9B, FIG. 9C, FIG. 9D, FIG. 9E, FIG. 9F, FIG. 9G, FIG. 9H,FIG. 9I, FIG. 9J, FIG. 9K, and FIG. 9L are aberration diagrams at thetime of infinite object point focusing of the zoom lens according to theexample 4;

FIG. 10A, FIG. 10B, FIG. 10C, FIG. 10D, FIG. 10E, FIG. 10F, FIG. 10G,FIG. 10H, FIG. 10I, FIG. 10J, FIG. 10K, and FIG. 10L are aberrationdiagrams at the time of infinite object point focusing of the zoom lensaccording to the example 5;

FIG. 11 is a cross-sectional view showing an amount of asphericaldeviation of an aspherical lens;

FIG. 12 is a diagram for explaining ω_(W);

FIG. 13 is a cross-sectional view of an image pickup apparatus;

FIG. 14 is a front perspective view showing an appearance of the imagepickup apparatus;

FIG. 15 is a rear perspective view of the image pickup apparatus; and

FIG. 16 is a block diagram of a configuration of an internal circuit ofmain components of the image pickup apparatus.

DETAILED DESCRIPTION OF THE INVENTION

Exemplary embodiments and examples of a zoom lens and an image pickupapparatus using the same will be described below in detail by referringto the accompanying diagrams. However, the present invention is notrestricted to the embodiments and examples described below.

In a zoom lens according to the present embodiment, the overall lengthof the zoom lens is shortened, and a half angle of view of 33 degrees,and furthermore more than 36 degrees, is secured at a wide angle end,and a zooming ratio more than 2.8 times is achieved. In order to achievethese specifications, in the zoom lens according to the presentembodiment, an optical system with the number of lenses that will nothinder the shortening of the overall length of the zoom lens, and asymmetrical arrangement of refractive power, has been realized.

More specifically, in the zoom lens according to the present embodiment,in order to prevent hindering of shortening of the overall length of thezoom lens, the number of lenses in each lens unit is reduced to besmall, and accordingly, an overall thickness of lenses in each lens unitis made small. Moreover, by imparting a refractive power arrangement ofa negative refractive power, a positive refractive power, and a negativerefractive power in order from an object side to an image side, theoptical system is built such that the refractive power arrangement fromthe wide angle end to a telephoto end comes closer to a symmetricalform.

An arrangement of the zoom lens according to the present embodiment willbe described below. Firstly, the basic arrangement will be described.

In the basic arrangement of the zoom lens according to the presentembodiment, the zoom lens includes in order from the object side to theimage side, a first lens unit having a negative refractive power, asecond lens unit having a positive refractive power, and a third lensunit having a negative refractive power. At the time of zooming,distances between the lens units change, and a distance between thefirst lens unit and the second lens unit at a telephoto end is shorterthan a distance between the first lens unit and the second lens unit ata wide angle end. An aperture stop is disposed on the image side of animage-side surface of the first lens unit, and on the object side of animage-side surface of the second lens unit.

By making such an arrangement, from the wide angle end to the telephotoend, or in other words, in the total zoom range, it becomes easy to makean arrangement such that the refractive power arrangement becomes asymmetrical arrangement with the second lens unit (aperture stop) at thecenter. Therefore, even if the overall length of the zoom lens at thewide angle end is shortened by decreasing the number of lenses, it ispossible to suppress degradation of various aberrations due to decreasein the number of lenses. In such manner, in the basic arrangement,small-sizing of the optical system and securing a stable opticalperformance throughout the total zoom range are facilitated. The stableoptical performance means that the occurrence of various aberrations andfluctuation thereof are suppressed sufficiently.

Next, preferable arrangements and preferable conditional expressionswill be described below.

In the zoom lens according to the present embodiment, it is preferablethat the first lens unit includes in order from the object side to theimage side, an object-side sub lens unit and an image-side sub lensunit. Moreover, it is preferable that the object-side sub lens unit inthe first lens unit includes a first negative lens, and the image-sidesub lens unit in the first lens unit includes a second negative lens anda first positive lens.

By forming the object-side sub lens unit in the first lens unit by thefirst negative lens, and making the negative refractive power of thefirst negative lens large, it is possible to bring an entrance pupilcloser to the object side. By making such an arrangement, it is possibleto contribute to securing a large angle of view at the wide angle end,and making a diameter of the optical system small.

However, if the refractive power of the first negative lens is madelarge, an astigmatism is susceptible to occur near the wide angle end,and a spherical aberration and a coma are susceptible to occur near thetelephoto end. By letting the image-side sub lens unit, have theabovementioned arrangement, it is possible to suppress an occurrence ofaberration in the entire first lens unit. As a result, a stable opticalperformance in the total zoom range is achieved.

It is preferable to let the first negative lens to be a negativemeniscus lens having a convex surface directed toward the object side.By making such an arrangement, an amount of the astigmatism and the comaoccurring in the first negative lens is reduced, thereby reducingaberrations occurring in the first lens unit.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the second lens unit includes in order from the objectside to the image side, an object-side sub lens unit having a positiverefractive power and an image-side sub lens unit. Moreover, it ispreferable that the object-side sub lens unit in the second lens unitincludes one lens component, and in the lens component, only twosurfaces, namely, an object-side surface and an image-side surface, arein contact with air in the optical path.

The second lens unit is positioned near the aperture stop. Therefore,the second lens unit is involved largely in the occurrence of thespherical aberration and the coma. Therefore, by including theobject-side sub lens unit and the image-side sub lens unit in the secondlens unit as aforementioned, it is possible to negate the sphericalaberration and the coma occurred in the sub lens unit by two sub lensunits. In such manner, it is possible to adopt an arrangement whichenables to correct favorably the spherical aberration and the coma inthe second lens unit. Moreover, by securing appropriately an air spacebetween the two sub lens units, an effect of correction of astigmatismis achieved.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the image-side sub lens unit in the second lens unit hasa lens surface having a negative refractive power, and a positive lensthat is disposed on the image side of the lens surface.

By making such an arrangement, it is possible to improve further thebalance of symmetry of the refractive power arrangement, or a balancerelated to a magnitude of the negative refractive power in particular.In such manner, by improving the balance of magnitude of the refractivepower, further improvement in the stable optical performance throughoutthe total zoom range is carried out while carrying out small-sizing ofthe optical system by making the refractive power of the second lensunit large.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (1) is satisfied.3.0<ΔD ₁₂ /ER _(S)<4.5  (1)

where,ΔD ₁₂ =D _(12W) −D _(12T),

D_(12W) denotes the distance between the first lens unit and the secondlens unit at the wide angle end,

D_(12T) denotes the distance between the first lens unit and the secondlens unit at the telephoto end,

both D_(12W) and D_(12T) are distances on an optical axis at the time ofinfinite object point focusing,

ER_(S) denotes the maximum radius of an opening of the aperture stop.

Conditional expression (1) is a conditional expression for small-sizingof the optical system, and is an expression that specifies a preferableamount of change in the distance (space) between the first lens unit andthe second lens unit.

By making so as not to fall below a lower limit value of conditionalexpression (1), even in a case of securing the required zooming ratio,such as zooming of 2.8 times or more, it is possible to suppress anincrease in the refractive power of each of the first lens unit and thesecond lens unit. Therefore, it is possible to reduce a fluctuation inthe spherical aberration at the time of zooming and a fluctuation in acurvature of field at the time of zooming even while suppressing anincrease in the number of lenses, in each of the first lens unit and thesecond lens unit.

Moreover, since it is possible to suppress the increase in the number oflenses, it is possible to reduce a thickness when collapsed, in a caseof using a collapsible type for accommodating the zoom lens. In suchmanner, by making so as not to fall below the lower limit value ofconditional expression (1), it is possible to contribute to small-sizingof the camera as well.

By making so as not to exceed an upper limit value of conditionalexpression (1), it is possible to let the distance between the firstlens unit and the second lens unit not to increase excessively. Bymaking such an arrangement, it is possible to contribute to shorteningthe overall length of the zoom lens.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (2) is satisfied.1.05<|f ₃ /f _(UN)21|<2.1  (2)

where,

f₃ denotes a focal length of the third lens unit, and

f_(UN21) denotes a focal length of the object-side sub lens unit in thesecond lens unit.

Conditional expression (2) is an expression which specifies a preferablerefractive power of the third lens unit.

By making so as not to fall below a lower limit value of conditionalexpression (2) or not to exceed an upper limit value of conditionalexpression (2), it is possible to maintain a favorable balance ofsymmetry of the refractive power arrangement and a favorable balance ofmagnitude of the negative refractive power in particular. By making suchan arrangement, it is possible to contribute to a favorable correctionof the spherical aberration and the curvature of field, and to secure awide angle of view at the wide angle end, and to secure a stable opticalperformance throughout the total zoom range.

In the zoom lens according to the present embodiment, it is preferablethat the following conditional expression (3) is satisfied.−0.9<SF _(2N)<1.5  (3)

where,SF _(2N)=(R _(2NO) +R _(2NI))/(R _(2NO) −R _(2NI)),

R_(2NO) denotes a paraxial radius of curvature of an object-side surfaceof the second negative lens in the first lens unit, and

R_(2NI) denotes a paraxial radius of curvature of an image-side surfaceof the second negative lens in the first lens unit.

By making so as not to fall below a lower limit value of conditionalexpression (3), it is possible to prevent an edge (peripheral portion)on an object-side surface of the second negative lens from sticking outexcessively toward the first negative lens. Accordingly, since itbecomes easy to bring the second negative lens closer to the firstnegative lens, it is possible to make a distance between the firstnegative lens and the second negative lens small. By making such anarrangement, it is possible to contribute to small-sizing of the firstlens unit.

By making so as not to exceed an upper limit value of conditionalexpression (3), it is made easy to achieve an effect of correctingsufficiently the astigmatism of an object-side surface of the secondnegative lens.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that conditional expression (4) is satisfied.1.2<ΔD ₁₂ /IH _(MAX)<1.85  (4)

where,ΔD ₁₂ =D _(12W) −D _(12T),

D_(12W) denotes the distance between the first lens unit and the secondlens unit at the wide angle end,

D_(12T) denotes the distance between the first lens unit and the secondlens unit at the telephoto end,

both D_(12W) and D_(12T) are distances on an optical axis at the time ofinfinite object point focusing, and

IH_(MAX) denotes the maximum image height, and denotes the maximum valuein a case in which, the maximum image height changes with zooming.

A technical significance of conditional expression (4) is same as atechnical significance of conditional expression (1). Therefore, thetechnical significance of conditional expression (4) is omitted.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that either of the following conditional expressions (5) or(5′) is satisfied.0.8<|f ₃ /f _(W)|<2.5  (5)1.1<|f ₃ /f _(W)|<1.9  (5′)

where,

f₃ denotes a focal length of the third lens unit, and

f_(W) denotes a focal length of the overall zoom lens system at the timeof infinite object point focusing at the wide angle end.

A technical significance of conditional expressions (5) and (5′) is sameas a technical significance of conditional expression (2). Therefore,description of the technical significance of (5) and (5′) is omitted.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that one of the following conditional expressions (6) or (6′)is satisfied.0.43<Σ_(2G) /f ₂<0.78  (6)0.45<Σ_(2G) /f ₂<0.75  (6′)

where,

Σ_(2G) denotes a thickness on an optical axis of the second lens unit,and

f₂ denotes a focal length of the second lens unit.

By making so as not to fall below a lower limit value of conditionalexpression (6), it becomes easy to suppress the tendency of thecurvature of field becoming excessive. Accordingly, it is made easy tosuppress an increase in the curvature of field throughout the total zoomrange. Moreover, it becomes easy to secure sufficiently the refractivepower of the second lens unit. By making such an arrangement, it ispossible to contribute to the shortening of the overall length of thezoom lens.

By making so as not to exceed an upper limit value of conditionalexpression (6), it is possible to suppress an increase in thickness ofthe second lens unit. By making such an arrangement, it is possible tocontribute to the shortening of the overall length of the zoom lens.

A technical significance of conditional expression (6′) is same as atechnical significance of conditional expression (6). Therefore,description of the technical significance of conditional expression (6′)is omitted.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (7) is satisfied.0.6<f _(UN21) /f ₂<1.8  (7)

where,

f_(UN21) denotes a focal length of the object-side sub lens unit in thesecond lens unit, and

f₂ denotes a focal length of the second lens unit.

By making so as not to fall below a lower limit value of conditionalexpression (7), it is possible to suppress occurrence of the sphericalaberration and the coma in the object-side sub lens unit in the secondlens unit. Moreover, even if the spherical aberration and the comaoccur, since it is possible to suppress an amount of the sphericalaberration and the coma that occurs, it becomes easy to negate thespherical aberration and the coma the image-side sub lens unit. Bymaking such an arrangement, it is possible to contribute to animprovement of the optical performance.

By making so as not to exceed an upper limit value of conditionalexpression (7), it becomes easy to make the refractive power of thesecond lens unit large. By making such an arrangement, it is possible tocontribute to the shortening of the overall length of the zoom lens.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (8) is satisfied.1.17<|f ₃ /f ₂|<1.95  (8)

where,

f₂ denotes a focal length of the second lens unit, and

f₃ denotes a focal length of the third lens unit.

By making so as not to fall below a lower limit value of conditionalexpression (8), it is possible to make the refractive power of the thirdlens unit moderately small. By making such an arrangement, it ispossible to contribute to the shortening of the overall length of thezoom lens.

By making so as not to exceed an upper limit value of conditionalexpression (8), it is possible to secure sufficiently a correction ofthe spherical aberration and the coma that occurs in the third lensunit. Accordingly, it becomes easy to achieve the stable opticalperformance throughout the total zoom range.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (9) is satisfied.1.15<f ₂ /IH _(MAX)<1.5  (9)

where,

f₂ denotes a focal length of the second lens unit, and

IH_(MAX) denotes the maximum image height, and denotes the maximum valuein a case in which, the maximum image height changes with zooming.

In the second lens unit, the spherical aberration and the coma aresusceptible to occur. Therefore, by making so as not to fall below alower limit value of conditional expression (9), it becomes easy tosuppress the spherical aberration and the coma from occurring, with thesmall number of lenses. By making such an arrangement, it is possible tocontribute to small-sizing in an optical direction of the second lensunit.

By making so as not to exceed an upper limit value of conditionalexpression (9), it is possible to contribute to achieve both of securingthe required zooming ratio, such as zooming ratio of 2.8 times or more,and shortening the overall length of the zoom lens.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (10) is satisfied.1.5<f _(UN21) /ER _(S)<3.9  (10)

where,

f_(UN21) denotes a focal length of the object-side sub lens unit in thesecond lens unit, and

ER_(S) denotes the maximum radius of an opening of the aperture stop.

A technical significance of conditional expression (10) is same as atechnical significance of conditional expression (7). Therefore,description of the technical significance of conditional expression (10)is omitted.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (11) is satisfied.3<LTL _(min) /fb _(LTLmin)<13  (11)

where,

LTL_(min) denotes a sum of an overall length of the zoom lens at thetime of infinite object point focusing and an air-converted back focus,and is the minimum value thereof in a case in which, the overall lengthchanges with zooming,

the overall length is a distance on an optical axis from a refractingsurface of the zoom lens nearest to the object side and a refractingsurface of the zoom lens nearest to the image side, and

fb_(LTLmin) denotes the air-converted back focus at LTL_(min).

For securing the required zooming ratio such as 2.8 times or more, avariable space corresponding to the zooming ratio, or in other words, aspace for the lens units to move corresponding to the zooming ratio isnecessary. By making so as not to fall below a lower limit value ofconditional expression (11), it is made easy to secure the requiredvariable space corresponding to the zooming ratio.

By making so as not to exceed an upper limit value of conditionalexpression (11), shortening of the overall length of the zoom lens iscarried out. Moreover, in a case in which, the zoom lens is used for aninterchangeable lens, the required back focus is secured such that thereis no interference (collision) with a camera main-body.

The basic arrangement, preferable arrangements, and preferableconditional expressions have been described above. By combining thepreferable arrangements and the preferable conditional expressionsappropriately with the basic arrangement, it is possible to form thezoom lens according to the present embodiment more specifically. Themore specific zoom lens according to the present embodiment is asfollows. Since the technical significance of each arrangement and eachconditional expression, have already been described, the descriptionthereof is omitted below.

A zoom lens according to a first embodiment of the present inventionincludes in order from an object side to an image side, a first lensunit having a negative refractive power, a second lens unit having apositive refractive power, and a third lens unit having a negativerefractive power, and at the time of zooming, distances between the lensunits change, and a distance between the first lens unit and the secondlens unit at a telephoto end is shorter than a distance between thefirst lens unit and the second lens unit at a wide angle end, and anaperture stop is disposed on the image side of an image-side surface ofthe first lens unit, and on the object side of an image-side surface ofthe second lens unit, and the second lens unit includes in order fromthe object side to the image side, an object-side sub lens unit having apositive refractive power and an image-side sub lens unit, and theobject-side sub lens unit in the second lens unit includes one lenscomponent, and in the lens component, only two surfaces, namely, anobject-side surface and an image-side surface, are in contact with airin an optical path, and the following conditional expressions (1) and(2) are satisfied.3.0<ΔD ₁₂ /ER _(S)<4.5  (1)1.05<|f ₃ /f _(UN21)|<2.1  (2)

A zoom lens according to a second embodiment of the present inventionincludes in order from an object side to an image side, a first lensunit having a negative refractive power, a second lens unit having apositive refractive power, and a third lens unit having a negativerefractive power, and at the time of zooming, distances between the lensunits change, and a distance between the first lens unit and the secondlens unit at a telephoto end is shorter than a distance between thefirst lens unit and the second lens unit at a wide angle end, and anaperture stop is disposed on the image side of an image-side surface ofthe first lens unit, and on the object side of an image-side surface ofthe second lens unit, and the first lens unit includes in order from theobject side to the image side, an object-side sub lens unit and animage-side sub lens unit, and the object-side sub lens unit in the firstlens unit includes a first negative lens, and the image-side sub lensunit in the first lens unit includes a second negative lens and a firstpositive lens, and the second lens unit includes in order from theobject side to the image side, an object-side sub lens unit having apositive refractive power, and an image-side sub lens unit, and theobject-side sub lens unit in the second lens unit includes one lenscomponent, and in the lens component, only two surfaces, namely, anobject-side surface and an image-side surface, are in contact with airin an optical path, and the following conditional expressions (1) and(3) are satisfied.3.0<ΔD ₁₂ /ER _(S)<4.5  (1)−0.9<SF _(2N)<1.5  (3)

A zoom lens according to a third embodiment of the present inventionincludes in order from an object side to an image side, a first lensunit having a negative refractive power, a second lens unit having apositive refractive power, and a third lens unit having a negativerefractive power, and at the time of zooming, distances between the lensunits change, and a distance between the first lens unit and the secondlens unit at a telephoto end is shorter than a distance between thefirst lens unit and the second lens unit at a wide angle end, and anaperture stop is disposed on the image side of an image-side surface ofthe first lens unit, and on the object side of an image-side surface ofthe second lens unit, and the following conditional expressions (4) and(5′) are satisfied.1.2<ΔD ₁₂ /IH _(MAX)<1.85  (4)1.1<|f ₃ /f _(W)|<1.9  (5′)

A zoom lens according to a fourth embodiment of the present inventionincludes in order from an object side to an image side, a first lensunit having a negative refractive power, a second lens unit having apositive refractive power, and a third lens unit having a negativerefractive power, and the time of zooming, distances between the lensunits change, and a distance between the first lens unit and the secondlens unit at a telephoto end is shorter than a distance between thefirst lens unit and the second lens unit at a wide angle end, and anaperture stop is disposed on the image side of an image-side surface ofthe first lens unit, and on the object side of an image-side surface ofthe second lens unit, and the following conditional expressions (4) and(6) are satisfied.1.2<ΔD ₁₂ /IH _(MAX)<1.85  (4)0.43<Σ_(2G) /f ₂<0.78  (6)

A zoom lens according to a fifth embodiment of the present inventionincludes in order from an object side to an image side, a first lensunit having a negative refractive power, a second lens unit having apositive refractive power, and a third lens unit having a negativerefractive power, and at the time of zooming, distances between the lensunits change, and a distance between the first lens unit and the secondlens unit at a telephoto end is shorter than a distance between thefirst lens unit and the second lens unit at a wide angle end, and anaperture stop is disposed on the image side of an image-side surface ofthe first lens unit, and on the object side of an image-side surface ofthe second lens unit, and the second lens unit includes in order fromthe object side to the image side, an object-side sub lens unit having apositive refractive power, and an image-side sub lens unit, and theobject-side sub lens unit in the second lens unit includes one lenscomponent, and in the lens component, only two surfaces, namely, anobject-side surface and an image-side surface, are in contact with airin an optical path, and the following conditional expressions (7), (8),and (9) are satisfied.0.6<f _(UN21) /f ₂<1.8  (7)1.17<|f ₃ /f ₂|<1.95  (8)1.15<f ₂ /IH _(MAX)<1.5  (9)

A zoom lens according to a sixth embodiment of the present inventionincludes in order from an object side to an image side, a first lensunit having a negative refractive power, a second lens unit having apositive refractive power, and a third lens unit having a negativerefractive power, and at the time of zooming, distances between the lensunits change, and a distance between the first lens unit and the secondlens unit at a telephoto end is shorter than a distance between thefirst lens unit and the second lens unit at a wide angle end, and anaperture stop is disposed on the image side of an image-side surface ofthe first lens unit, and on the object side of an image-side surface ofthe second lens unit, and the first lens unit includes in order from theobject side to the image side, an object-side sub lens unit and animage-side sub lens unit, and the object-side sub lens unit in the firstlens unit includes a first negative lens, and the image-side sub lensunit in the first lens unit includes a second negative lens and a firstpositive lens, and the second lens unit includes in order from theobject side to the image side, an object-side sub lens unit having apositive refractive power, and an image-side sub lens unit, and theobject-side sub lens unit in the second lens unit includes one lenscomponent, and in the lens component, only two surfaces, namely, anobject-side surface and an image-side surface, are in contact with airin an optical path, and the image-side sub lens unit in the second lensunit includes a lens surface having a negative refractive power and apositive lens which is disposed on the image side of the lens surface,and the following conditional expressions (3), (10), and (11) aresatisfied.−0.9<SF ₂ N<1.5  (3)1.5<f _(UN)21/ER _(S)<3.9  (10)3<LTL _(min) /fb _(LTLmin)<13  (11)

A zoom lens according to a seventh embodiment of the present inventionincludes in order from an object side to an image side, a first lensunit having a negative refractive power, a second lens unit having apositive refractive power, and a third lens unit having a negativerefractive power, and at the time of zooming, distances between the lensunits change, and a distance between the first lens unit and the secondlens unit at a telephoto end is shorter than a distance between thefirst lens unit and the second lens unit at a wide angle end, and anaperture stop is disposed on the image side of an image-side surface ofthe first lens unit, and on the object side of an image-side surface ofthe second lens unit, and the second lens unit includes in order fromthe object side to the image side, an object-side sub lens unit having apositive refractive power, and an image-side sub lens unit, and theobject-side sub lens unit in the second lens unit includes one lenscomponent, and in the lens component, only two surfaces, namely, anobject-side surface and an image-side surface, are in contact with airin an optical path, and the following conditional expressions (2) and(4) are satisfied.1.05<|f ₃ /f _(UN21)|<2.1  (2)1.2<ΔD ₁₂ /IH _(MAX)<1.85  (4)

Moreover, for the zoom lenses according to the embodiments from thefirst embodiment to the seventh embodiment (hereinafter, appropriatelycalled as ‘the zoom lens according to the present embodiment’), it ispossible to combine the following arrangements and conditionalexpressions.

In the zoom lens according to the present embodiment, it is preferablethat the zoom lens includes a fourth lens unit having a positiverefractive power, disposed on the image side of the third lens unit, andat the time of zooming, a distance between the third lens unit and thefourth lens unit changes.

When such an arrangement is made, an optical system in which, the thirdlens unit having a negative refractive power and the fourth lens unithaving a positive refractive power are combined, becomes a magnifyingoptical system which magnifies an image formed at a lens unit on theobject side of the third lens unit. Accordingly, a diameter of the firstlens unit is made small. Moreover, it becomes easy to move an exit pupilaway from an image pickup surface (image plane). By making such anarrangement, it is possible to contribute to improve a variation in anamount of light at a central area of an image and an amount of light ata peripheral area of the image.

Moreover, in the zoom lens according to the present embodiment, it ispreferable to let a lens surface nearest to the object side of thefourth lens unit to be a concave surface directed toward the objectside, and to let a lens surface nearest to the image side of the fourthlens unit to be a convex surface directed toward the image side. Bymaking such an arrangement, it is possible to contribute to securingstable optical performance throughout the total zoom range.

In the zoom lens according to the present embodiment, it is preferablethat a distance between the third lens unit and the fourth lens unit atthe telephoto end is longer than a distance between the third lens unitand the fourth lens unit at the wide angle end.

By making such an arrangement, it is possible to contribute to securingthe required zooming ratio.

In the zoom lens according to the present embodiment, it is preferablethat the fourth lens unit is stationary at the time of zooming.

By letting the fourth lens unit to be stationary at the time of zooming,it becomes easy to simplify a structure of a drive mechanism. By makingsuch an arrangement, it is possible to contribute to small-sizing of theoptical system. Moreover, it is also possible to contribute to noisereduction when the zoom lens is operated.

Moreover, in the zoom lens according to the present invention, it ispreferable that the total number of lens units in the zoom lens is four,namely, the first lens unit, the second lens unit, the third lens unit,and the fourth lens unit.

By making the zoom lens a four-unit zoom lens, it becomes easy tosimplify an arrangement of a holding member. By making such anarrangement, it is possible to contribute to small-sizing of the opticalsystem.

In the zoom lens according to the present embodiment, it is preferablethat the object-side sub lens unit and the image-side sub lens unit inthe second lens unit are disposed such that, an axial air space betweenthe object-side sub lens unit and the image-side sub lens unit is themaximum in the second lens unit.

By making such an arrangement, it is possible to contribute to favorablecorrection of various aberrations occurring in the second lens unit. Theimage-side sub lens unit may include a plurality of lens components. Inthis case, the second lens unit is arranged to have a plurality of axialair spaces. Therefore, when the abovementioned arrangement is made, afavorable aberration correction in the second lens unit becomespossible.

Moreover, in the zoom lens according to the embodiment, it is preferablethat the image-side sub lens unit in the second lens unit includes onelens component, and in the lens component, only two surfaces, namely,the object-side surface and the image-side surface, are in contact withair in the optical path.

By making such an arrangement, it is possible to contribute tosmall-sizing of the second lens unit.

In the zoom lens according to the present embodiment, it is preferablethat the following conditional expression (5) is satisfied.0.8<|f ₃ /f _(W)|<2.5  (5)

where,

f₃ denotes a focal length of the third lens unit, and

f_(W) denotes a focal length of the overall zoom lens system at the timeof infinite object point focusing at the wide angle end.

The technical significance of conditional expression (5) is as alreadyexplained.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (12) is satisfied.−20.0%<DT _(W)<−6.0%  (12)

where,DT _(W) ={IH _(W) −f _(W)×tan(ω_(W))}/{f _(W)×tan(ω_(W))}×100(%),

f_(W) denotes a focal length of the overall zoom lens system at the timeof infinite object point focusing at the wide angle end,

IH_(W) denotes the maximum image height at the time of infinite objectpoint focusing at the wide angle end, and

ω_(W) denotes a half angle of view at the time of infinite object pointfocusing at the wide angle end.

It is preferable to reduce a distortion of image by making so an not tofall below a lower limit value of conditional expression (12). Moreover,by making so as not to fall below the lower limit value of conditionalexpression (12), even in a case in which, the distortion at the wideangle end has been corrected electrically, it is possible to suppressdegradation of resolution at the periphery of an image after correction.

By making so as not to exceed an upper limit value of conditionalexpression (12), it is possible to contribute to a favorable correctionof astigmatism and small-sizing of the first lens unit.

In the zoom lens according to the present embodiment, it is preferablethat the second lens unit includes in order from the object side to theimage side, the object-side sub lens unit having a positive refractivepower and the image-side sub lens unit, and the object-side lens unit inthe second lens unit includes one lens component, and in the lenscomponent, only two surfaces, namely, the object-side surface and theimage-side surface, are in contact with air in the optical path, and thefollowing conditional expression (13) is satisfied.−1.5<SF _(UN21)<0.5  (13)

where,SF _(UN21)=(R _(UN21O) +R _(UN21I))/(R _(UN21O) −R _(UN21I))

R_(UN21O) denotes a paraxial radius of curvature of an object-sidesurface of the object-side sub lens unit in the second lens unit, and

R_(UN21I) denotes a paraxial radius of curvature of an image-sidesurface of the object-side sub lens unit in the second lens unit.

The spherical aberration and the coma are susceptible to occur at asurface of incidence of the object-side sub lens unit in the second lensunit. Therefore, by making so as not to fall below a lower limit valueof conditional expression (13), it is possible to suppress theoccurrence of the spherical aberration and the coma. By making such anarrangement, it is possible to contribute to securing a favorableoptical performance, particularly near the telephoto end. The favorableoptical performance means that the occurrence of various aberrations issuppressed sufficiently.

By making so as not to exceed an upper limit value of conditionalexpression (13), a principal point of the second lens unit is not drawnexcessively toward the image side, thereby making it is easy to securethe required zooming ratio.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (14) is satisfied.0.38<Σ_(2G) /f _(W)<0.75  (14)

where,

Σ_(2G) denotes a thickness of the second lens unit on an optical axis,and

f_(W) denotes a focal length of the overall zoom lens system at the timeof infinite object point focusing at the wide angle end.

The curvature of field is reduced by making so as not to fall below alower limit value of conditional expression (14), thereby making it easyto carry out the correction of the curvature of field throughout thetotal zoom range.

The thickness of the second lens unit is made small by making so as notto exceed an upper limit value of conditional expression (14), therebymaking a collapsed thickness is reduced, in a case of using acollapsible type for accommodating the zoom lens. Moreover, by makingsuch an arrangement, small-sizing of camera is carried out.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the second lens unit includes in order from the objectside to the image side, the object-side sub lens unit having a positiverefractive power and the image-side sub lens unit, and the object-sidesub lens unit in the second lens unit includes one lens component, andin the lens component, only two surfaces, namely, the object-sidesurface and the image-side surface, are in contact with air in theoptical path, and the image-side sub lens unit in the second lens unitincludes a lens surface having a negative refractive power, and apositive lens which is disposed on the image side of the lens surface.

A technical significance of such arrangement is as already explained.

In the zoom lens according to the present embodiment, it is preferablethat the following conditional expression (8) is satisfied.1.17<|f ₃ /f ₂|<1.95  (8)

where,

f₂ denotes a focal length of the second lens unit, and

f₃ denotes a focal length of the third lens unit.

The technical significance of conditional expression (8) is as alreadyexplained.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (15) is satisfied.1.3<|f ₃ /IH _(MAX)|<2.5  (15)

where,

f₃ denotes the focal length of the third lens unit, and

IH_(MAX) denotes the maximum image height, and denotes the maximum valuein a case in which, the maximum image height changes with zooming.

A technical significance of conditional expression (15) is same as thetechnical significance of conditional expression (8). Therefore, theexplanation of the technical significance of conditional expression (15)is omitted.

In the zoom lens according to the present embodiment, it is preferablethat the third lens unit includes a lens having a specific gravity morethan 0.9 g/cm³ and less than 1.3 g/cm³.

It is possible to make the involvement of the third lens unit in zoomingcomparatively smaller. Therefore, it is preferable to carry outreduction of image blur due to focusing and camera shake by using thethird lens unit. In focusing, it is preferable to move the third lensunit in an optical axial direction. Moreover, for reducing the imageblur, it is preferable to move the third lens unit in a directionorthogonal to the optical axis (shifting movement).

Here, by the third lens unit satisfying the abovementioned condition ofspecific gravity, it is possible to secure light weight and highrigidity of the third lens unit. By making such an arrangement, afollowability of the third lens unit at the time of moving is improved,and accordingly, the reduction of the focusing and image blur isaccelerated.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the second lens unit includes a negative lens, and apositive lens that satisfies the following conditional expression (16).63<ν_(p1)<96  (16)

where,

ν_(p1) denotes Abbe's number for a d-line of any of the positive lensesin the second lens unit.

Since the second lens unit is close to the aperture stop, an effect onthe spherical aberration for each color is large. For correction of alongitudinal chromatic aberration, it is preferable to make a dispersionin a lens having a positive refractive power small, and a dispersion ina lens having a negative refractive power large. However, since the lenswith a large dispersion also has a large anomalous dispersibility, in alens with an excessively large dispersion, it becomes difficult tocorrect the spherical aberration for each color. Therefore, bysatisfying conditional expression (16), it is possible to correct theseaberrations favorably.

By making so as not to fall below a lower limit value of conditionalexpression (16), since the dispersion in the positive lens can be madeto be low dispersion, it is possible to suppress an increase in theanomalous dispersibility of the negative lens relatively. By making suchan arrangement, it is possible to contribute to favorable correction ofchromatic aberration.

By making so as not to exceed an upper limit value of conditionalexpression (16), since it is possible to impart a dispersion of certainmagnitude to the positive lens, it is possible to reduce the abnormaldispersibility of the positive lens. By making such an arrangement, itis possible to contribute to favorable correction of the chromaticaberration.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the first lens unit includes in order from the objectside to the image side, an object-side sub lens unit and an image-sidesub lens unit, and the object-side sub lens unit in the first lens unitincludes a first negative lens, and the image-side sub lens unit in thefirst lens unit includes a second negative lens and a first positivelens.

A technical significance of such arrangement is as already explained.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (3) is satisfied.−0.9<SF _(2N)<1.5  (3)

where,SF _(2N)=(R _(2NO) +R _(2NI))/(R _(2NO) −R _(2NI)),

R_(2NO) denotes a paraxial radius of curvature of an object-side surfaceof the second negative lens in the first lens unit, and

R_(2NI) denotes a paraxial radius of curvature of an image-side surfaceof the second negative lens in the first lens unit.

A technical significance of conditional expression (3) is as alreadyexplained.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (17) is satisfied.0.6<fb _(W) /IH _(MAX)<1.8  (17)

where,

fb_(W) denotes an air-converted back-focus at the time of infiniteobject point focusing at the wide angle end, and

IH_(MAX) denotes the maximum image height, and denotes the maximum valuein a case in which, the maximum image height changes with zooming.

The overall zoom lens is drawn away from an image plane by making so annot to fall below a lower limit value of conditional expression (17),thereby making it becomes easy to draw the exit pupil away from theimage plane. Accordingly, since it becomes possible to make an angle ofincidence of a light ray incident on the image plane small, it ispossible to improve a variation in an amount of light at a central areaof an image and an amount of light at a peripheral area of the image.

By making so as not to exceed an upper limit value of conditionalexpression (17), it is possible to contribute to shortening the overalllength of the zoom lens and securing a wide angle of view at the wideangle end.

In the zoom lens according to the present embodiment, it is preferablethat the following conditional expression (18) is satisfied.0.4<f ₁ /f ₃<1.2  (18)

where,

f₁ denotes a focal length of the first lens unit, and

f₃ denotes a focal length of the third lens unit.

An increase in the negative refractive power of the first lens unit issuppressed by making so as not to fall below a lower limit value ofconditional expression (18), thereby making an arrangement such that nolarge negative distortion occurs even when small-sizing of the opticalsystem is carried out.

An increase in the negative refractive power of the third lens unit issuppressed by making so as not to exceed an upper limit value ofconditional expression (18), thereby making an arrangement such that nolarge positive distortion occurs even when small-sizing of the opticalsystem is carried out. Moreover, it becomes easy to reduce an occurrenceof a chromatic aberration of magnification due to the third lens unit.By making such an arrangement, it is possible to contribute to reductionin the number of lenses in the third lens unit and small-sizing of theoptical system.

In the zoom lens according to the present embodiment, it is preferablethat the following conditional expression (6′) is satisfied.0.45<Σ_(2G) /f ₂<0.75  (6′)

where,

Σ_(2G) denotes a thickness on an optical axis of the second lens unit,and

f₂ denotes a focal length of the second lens unit.

A technical significance of conditional expression (6′) is same as thetechnical significance of conditional expression (6). Therefore,explanation of the technical significance of conditional expression (6′)is omitted.

In the zoom lens according to the present embodiment, it is preferablethat the following conditional expression (7) is satisfied.0.6<f _(UN21) /f ₂<1.8  (7)

where,

f_(UN21) denotes a focal length of the object-side sub lens unit in thesecond lens unit,

f₂ denotes a focal length of the second lens unit.

The technical significance of conditional expression (7) is as alreadyexplained.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (19) is satisfied.3<LTL _(W) /fb _(W)<13  (19)

where,

LTL_(W) denotes a sum of an overall length of the zoom lens at the timeof infinite object point focusing at the wide angle end and anair-converted back focus,

the overall length is a distance on an optical axis from a refractingsurface of the zoom lens nearest to the object side and a refractingsurface of the zoom lens nearest to the image side, and

fb_(W) denotes the air-converted back focus at LTL_(W).

A technical significance of conditional expression (19) is same as thetechnical significance of conditional expression (11). Therefore,explanation of the technical significance of conditional expression (19)is omitted.

In the zoom lens according to the present embodiment, it is preferablethat the following conditional expression (20) is satisfied.0.6<f _(UN21) /f _(W)<1.9  (20)

where,

f_(UN21) denotes a focal length of the object-side sub lens unit in thesecond lens unit, and

f_(W) denotes a focal length of the overall zoom lens system at the timeof infinite object point focusing at the wide angle end.

A technical significance of conditional expression (20) is same as thetechnical significance of conditional expression (10). Therefore,explanation of the technical significance of conditional expression (20)is omitted.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (20′) is satisfied.0.6<f _(UN21) /f _(W)<1.6  (20′)

where,

f_(UN21) denotes a focal length of the object-side sub lens unit in thesecond lens unit, and

f_(W) denotes a focal length of the overall zoom lens system at the timeof infinite object point focusing at the wide angle end.

A technical significance of conditional expression (20′) is same as thetechnical significance of conditional expression (20). Therefore,explanation of the technical significance of conditional expression(20′) is omitted.

In the zoom lens according to the present embodiment, it is preferablethat the following conditional expression (21) is satisfied.0.35<ΔD ₁₂ /f _(T)<0.6  (21)

where,ΔD ₁₂ =D _(12W) −D _(12T),

D_(12W) denotes the distance between the first lens unit and the secondlens unit at the wide angle end,

D_(12T) denotes the distance between the first lens unit and the secondlens unit at the telephoto end,

both D_(12W) and D_(12T) are distances on an optical axis at the time ofinfinite object point focusing, and

f_(T) denotes a focal length of the overall zoom lens system at the timeof infinite object point focusing at the telephoto end.

A technical significance of conditional expression (21) is same as thetechnical significance of conditional expression (1). Therefore,explanation of the technical significance of conditional expression (21)is omitted.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the following conditional expression (22) is satisfied.0.35<|f ₃ /ER _(S)|<1.05  (22)

where,

f₃ denotes the focal length of the third lens unit, and

ER_(S) denotes the maximum radius of an opening of the aperture stop.

A technical significance of conditional expression (22) is same as thetechnical significance of conditional expression (3). Therefore,explanation of the technical significance of conditional expression (22)is omitted.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that the first lens unit includes a plastic aspherical lenswhich satisfies the following conditional expression (23).0.0001<|ASP _(O) −ASP _(I) |/IH _(33W)<0.02  (23)

where,

IH_(33W) denotes a distance from an optical axis of a position at which,a principal ray intersects with a paraxial image plane such that, anincidence-side half angle of view of the zoom lens at the time ofinfinite object point focusing at the wide angle end becomes 33°.

ASP_(O) denotes an amount of aspherical deviation at a position atwhich, a distance of an object-side surface of the plastic asphericallens from the optical axis becomes IH_(33W),

ASP_(I) denotes an amount of aspherical deviation at a position atwhich, a distance of an image-side surface of the plastic asphericallens from the optical axis becomes IH_(33W), and

the amount of aspherical deviation is a distance along an optical axialdirection, from a reference spherical surface for which, a vertex of asurface intended is let to be the vertex, and a radius of curvature islet to be same as a paraxial radius of curvature of the surfaceintended, up to the surface intended, and a case in which, the intendedsurface is on the image side with respect to the reference sphericalsurface is let to have a positive sign.

The first lens unit, in particular, contributes to a favorablecorrection of the curvature of field near the wide angle end. Therefore,the effect of correction of the curvature of field is improved furtherby using the aspherical lens in the first lens unit. Moreover, a size ina radial direction of the first lens unit is larger as compared to asize of other lens units. Therefore, by using the plastic asphericallens in the first lens unit, an increase in a lens-cost is alsosuppressed while achieving an effect of the aspheric surface.

However, since a change in a surface shape according to temperature ismore for the plastic lens than for a glass, the curvature of field dueto a change in temperature occurs. Therefore, while achieving the effectof the aspheric surface by making so as not to fall below a lower limitvalue of conditional expression (23), and a fluctuation in aberrationdue to the change in temperature is suppressed by making so as not toexceed an upper limit value of conditional expression (23).

The amount of aspherical deviation, as shown in FIG. 11, is a distancefrom a reference spherical surface up to an aspheric surface, measuredin a direction parallel to the optical axis, when a spherical surfacehaving a vertex same as a vertex of an aspheric surface, and for which,a radius of curvature is let to be same as the paraxial radius ofcurvature of the aspheric surface, and a direction toward the image(rightward direction in the diagram) is let to have a positive sign.

It is preferable that a coefficient of thermal expansion α of a plasticmaterial to be used for the plastic lens satisfies the followingconditional expression.2e ⁻⁵ μm/° C.<α<8e⁻⁵ μm/° C.

Here, the coefficient of thermal expansion α means that when there is arise in temperature by 1° C. per 1 m, the dimension changes by α μm.

By satisfying the abovementioned conditional expression, it becomes easyto facilitate achieving both of ease of molding the lens and suppressingthe fluctuation in aberration due to the change in temperature.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that both the object-side surface and the image-side surfaceof the plastic aspherical lens are aspheric surfaces.

By making such an arrangement, the function of correction of aberrationby the aspheric surface is all the more improved.

Moreover, in the zoom lens according to the present embodiment, it ispreferable that at the wide angle end, a light ray of the half angle ofview 33° or more is capable of passing through the zoom lens, and thefollowing conditional expression (24) is satisfied.2.6<f _(T) /f _(W)<5.0  (24)

where,

f_(T) denotes a focal length of the overall zoom lens system at the timeof infinite object point focusing at the telephoto end, and

f_(W) denotes a focal length of the overall zoom lens system at the timeof infinite object point focusing at the wide angle end.

An appropriate zooming ratio is secured by making so as not to fallbelow a lower limit value of conditional expression (24), thereby makingselection of an appropriate angle of view according to variousphotography scenes is made possible.

By making so as not to exceed an upper limit value of conditionalexpression (24), it is possible to contribute to both of shortening theoverall length of the zoom lens and securing favorable opticalperformance.

In the zoom lens according to the present embodiment, it is preferablethat the second lens unit includes a single lens having a positiverefractive power which is disposed nearest to the object side in thesecond lens unit, and a cemented lens of a negative lens and a positivelens in order from the object side, and the aperture stop is positionedbetween the single lens and the cemented lens in the second lens unit.

By making such an arrangement, with a small number of lenses, therefractive power of the second lens unit is secured appropriately, and afavorable function of correcting aberration is secured as well.Moreover, since it is possible to dispose the aperture stop near acenter of the second lens unit, by making such an arrangement, it ispossible to contribute to securing symmetry of refractive powerarrangement with respect to the aperture stop, an in particular,symmetry of magnitude of the negative refractive power, as well as tocontribute all the more to securing favorable optical performance andsmall-sizing of the optical system.

At the time of zooming from the wide angle end to the telephoto end, thedistances between the lens units change. Here, it is preferable to letthe movement of each lens unit as follows at the time of zooming fromthe wide angle end to the telephoto end. It is preferable that the firstlens unit, after moving toward the image side, moves toward the objectside. It is preferable that the second lens unit G2 moves toward theobject side. It is preferable that the third lens unit G3 moves towardthe object side. Moreover, in a case in which, there is a lens unit onthe image side of the third lens unit, it is preferable that the lensunit on the image side of the third lens unit is fixed (is stationary).Moreover, it is preferable that the aperture stop (stop) moves towardthe object side together with the second lens unit G2.

Moreover, an image pickup apparatus according to the present embodimentincludes a zoom lens, and an image pickup element which has an imagepickup surface, and which converts an image formed on the image pickupsurface by the zoom lens to an electric signal, and the zoom lens is theaforementioned zoom lens.

By making such an arrangement, it is possible to provide an image pickupapparatus which includes a zoom lens in which, both favorable correctionof various aberrations and small-sizing of the optical system areachieved.

In a case in which, the zoom lens has a focusing function, theabovementioned arrangements will be let to be arrangements in a state ofbeing focused at an infinite object point.

It is preferable that a plurality of the abovementioned arrangements issimultaneously satisfied interactively. Moreover, an arrangement may bemade such that some of the arrangements are satisfied simultaneously.For instance, an arrangement may be made such that one of theabovementioned zoom lenses is used in one of the aforementioned zoomlenses or the image pickup apparatus.

Moreover, regarding the conditional expressions, an arrangement may bemade such that each conditional expression is satisfied separately. Whensuch an arrangement is made, it becomes easy to achieve the respectiveeffect, and therefore it is preferable.

For each conditional expression, the upper limit value or the lowerlimit value may be changed as follows. When the values are changed asgiven below, the effect of each conditional expression is all the moreassured, and therefore it is preferable.

For conditional expression (1), it is more preferable to let the lowerlimit value to be 3.3, and 3.6 is even more preferable.

Moreover, for conditional expression (1), it is more preferable to letthe upper limit value to be 4.3, and 4.2 is even more preferable.

For conditional expression (2), it is more preferable to let the lowerlimit value to be 1.2, and 1.3 is even more preferable.

Moreover, for conditional expression (2), it is more preferable to letthe upper limit value to be 1.9, and 1.8 is even more preferable.

For conditional expression (3), it is more preferable to let the lowerlimit value to be −0.5, and 0 is even more preferable.

Moreover, for conditional expression (3), it is more preferable to letthe upper limit value to be 1.3, and 0.6 is even more preferable.

For conditional expression (4), it is more preferable to let the lowerlimit value to be 1.35, and 1.5 is even more preferable.

Moreover, for conditional expression (4), it is more preferable to letthe upper limit value to be 1.75, and 1.7 is even more preferable.

For conditional expression (5), it is more preferable to let the lowerlimit value to be 1.1, and 1.2 is even more preferable.

Moreover, for conditional expression (5), it is more preferable to letthe upper limit value to be 1.9, and 1.8 is even more preferable.

For conditional expression (5′), it is more preferable to let the lowerlimit value to be 1.2.

Moreover, for conditional expression (5′), it is more preferable to letthe upper limit value to be 1.8.

For conditional expression (6), it is more preferable to let the lowerlimit value to be 0.45, and 0.5 is even more preferable.

Moreover, for conditional expression (6), it is more preferable to letthe upper limit value to be 0.75, and 0.7 is even more preferable.

For conditional expression (6′), it is more preferable to let the lowerlimit value to be 0.5.

Moreover, for conditional expression (6′), it is more preferable to letthe upper limit value to be 0.7.

For conditional expression (7), it is more preferable to let the lowerlimit value to be 0.8, and 0.85 is even more preferable.

Moreover, for conditional expression (7), it is more preferable to letthe upper limit value to be 1.6, and 1.4 is even more preferable.

For conditional expression (8), it is more preferable to let the lowerlimit value to be 1.25, and 1.3 is even more preferable.

Moreover, for conditional expression (8), it is more preferable to letthe upper limit value to be 1.8, and 1.75 is even more preferable.

For conditional expression (9), it is more preferable to let the lowerlimit value to be 1.18, and 1.20 is even more preferable.

Moreover, for conditional expression (9), it is more preferable to letthe upper limit value to be 1.40, and 1.35 is even more preferable.

For conditional expression (10), it is more preferable to let the lowerlimit value to be 1.8 or 2.0, and 2.5 is even more preferable.

Moreover, for conditional expression (10), it is more preferable to letthe upper limit value to be 3.85, and 3.5 is even more preferable.

For conditional expression (11), it is more preferable to let the lowerlimit value to be 3.5, and 3.9 is even more preferable.

Moreover, for conditional expression (11), it is more preferable to letthe upper limit value to be 8, and 4.5 is even more preferable.

For conditional expression (12), it is more preferable to let the lowerlimit value to be −17.0%, and −15.0% is even more preferable.

Moreover, for conditional expression (12), it is more preferable to letthe upper limit value to be −8.0%, and −10.0% is even more preferable.

For conditional expression (13), it is more preferable to let the lowerlimit value to be −1.3, and −1.35 is even more preferable.

Moreover, for conditional expression (13), it is more preferable to letthe upper limit value to be −0.1, and −0.5 is even more preferable.

For conditional expression (14), it is more preferable to let the lowerlimit value to be 0.45, and 0.54 is even more preferable.

Moreover, for conditional expression (14), it is more preferable to letthe upper limit value to be 0.72, and 0.7 is even more preferable.

For conditional expression (15), it is more preferable to let the lowerlimit value to be 1.5, and 1.6 is even more preferable.

Moreover, for conditional expression (15), it is more preferable to letthe upper limit value to be 2.45 or 2.4, and 2.3 is even morepreferable.

For conditional expression (16), it is more preferable to let the lowerlimit value to be 65, and 67 is even more preferable.

Moreover, for conditional expression (16), it is more preferable to letthe upper limit value to be 85, and 82 is even more preferable.

For conditional expression (17), it is more preferable to let the lowerlimit value to be 0.9, and 1.25 is even more preferable.

Moreover, for conditional expression (17) it is more preferable to letthe upper limit value to be 1.6, and 1.4 is even more preferable.

For conditional expression (18), it is more preferable to let the lowerlimit value to be 0.6, and 0.7 is even more preferable.

Moreover, for conditional expression (18), it is more preferable to letthe upper limit value to be 1.1, and 1.05 is even more preferable.

For conditional expression (19), it is more preferable to let the lowerlimit value to be 3.5, and 4.1 is even more preferable.

Moreover, for conditional expression (19), it is more preferable to letthe upper limit value to be 9 or 7, and 5 is even more preferable.

For conditional expression (20), it is more preferable to let the lowerlimit value to be 0.7, and 0.8 is even more preferable.

Moreover, for conditional expression (20), it is more preferable to letthe upper limit value to be 1.6 or 1.5, and 1.3 is even more preferable.

For conditional expression (20′), it is more preferable to let the lowerlimit value to be 0.7, and 0.8 is even more preferable.

Moreover, for conditional expression (20′), it is more preferable to letthe upper limit value to be 1.5, and 1.3 is even more preferable.

For conditional expression (21), it is more preferable to let the lowerlimit value to be 0.4, and 0.41 is even more preferable. Moreover, forconditional expression (21), it is more preferable to let the upperlimit value to be 0.55, and 0.46 is even more preferable.

For conditional expression (22), it is more preferable to let the lowerlimit value to be 0.40, and 0.45 is even more preferable.

Moreover, for conditional expression (22), it is more preferable to letthe upper limit value to be 0.95, and 0.85 is even more preferable.

For conditional expression (23), it is more preferable to let the lowerlimit value to be 0.0003, and 0.0005 is even more preferable.

Moreover, for conditional expression (23), it is more preferable to letthe upper limit value to be 0.015, and 0.01 is even more preferable.

For conditional expression (24), it is more preferable to let the lowerlimit value to be 2.7, and 2.8 is even more preferable.

Moreover, for conditional expression (24), it is more preferable to letthe upper limit value to be 4.0, and 3.5 is even more preferable.

ω_(W) (the maximum half angle of view when focused to an object atinfinity at the wide angle end) will be described by using FIG. 12. InFIG. 12, as to how, a zoom lens, an aperture stop, and an image pickupsurface are arranged on an optical axis is shown. A light ray which isincident on the zoom lens, upon passing through the aperture stop, isemerged from the zoom lens, and reaches the image pickup surface.

In FIG. 12, a light ray L shown by a solid line indicates a light raywhich reaches a point X on an effective image pickup area, from amonglight rays which pass through the center of the aperture stop. The pointX is a position farthest from the optical axis in the effective imagepickup area. Here, the effective image pickup area being an area, inwhich an object image is formed, the point X becomes the maximumimage-height position. In such manner, the light ray L is a light raywhich passes through the aperture stop, and which is incident on themaximum image-height position. Moreover, ω_(W) is a half angle of viewwith respect to an optical axis of light ray L, at the wide angle end.

Examples of the zoom lens used in the image pickup apparatus accordingto the present invention will be described below in detail by referringto the accompanying diagrams. However, the present invention is notrestricted to the examples described below.

Examples from an example 1 to an example 5 of the zoom lens will bedescribed below. Lens cross-sectional views of the examples from theexample 1 to the example 5 are shown in diagrams from FIG. 1A, FIG. 1B,and FIG. 1C to FIG. 5A, FIG. 5B, and FIG. 5C. In these diagrams, FIG.1A, FIG. 2A, FIG. 3A, FIG. 4A, and FIG. 5A are cross-sectional views ata wide angle end, FIG. 1B, FIG. 2B, FIG. 3B, FIG. 4B, and FIG. 5B, arecross-sectional views in an intermediate focal length state, and FIG.1C, FIG. 2C, FIG. 3C, FIG. 4C, and FIG. 5C are cross-sectional views ata telephoto end. Each of FIG. 1A, FIG. 1B, and FIG. 1C to FIG. 5A, FIG.5B, and FIG. 5C is a lens cross-sectional view when focused at aninfinite object point.

Moreover, a first lens unit is denoted by G1, a second lens unit isdenoted by G2, a third lens unit is denoted by G3, a fourth lens unit isdenoted by G4, an aperture stop is denoted by S, a flare aperture isdenoted by SF, and an image plane (image pickup surface) is denoted byI. Although it is not shown in the diagram, a flat and parallel platewhich forms a low-pass filter and a cover glass of an electronic imagepickup element may be disposed between the third lens unit G3 and theimage plane I. A wavelength region restricting coating which restrictsinfrared light may be applied to a surface of the flat and parallelplate. Moreover, a multilayer film for restricting wavelength region maybe applied to a surface of the cover glass. The cover glass C may beimparted an effect of a low-pass filter.

In the examples form the example 1 to the example 5, an image height issame at the wide angle end, in the intermediate focal length state, andat the telephoto end. However, the image height at the wide angle endmay be let to be small. This is because, letting the image at the wideangle end to be barrel-shaped, it is possible to correct distortion byconverting the barrel-shaped image to a rectangular image electrically.Details of correcting the distortion electrically are omitted.

The zoom lens according to the example 1, as shown in FIG. 1A, FIG. 1B,and FIG. 1C, includes in order from an object side, a first lens unit G1having a negative refractive power, a second lens unit G2 having apositive refractive power, a third lens unit G3 having a negativerefractive power, and a fourth lens unit G4 having a positive refractivepower. An aperture stop (stop) S is disposed in the second lens unit G2.

The first lens unit G1 includes a negative meniscus lens L1 having aconvex surface directed toward the object side, a biconcave negativelens L2, and a positive meniscus lens L3 having a convex surfacedirected toward the object side.

The second lens unit G2 includes a positive meniscus lens L4 having aconvex surface directed toward the object side, a negative meniscus lensL5 having a convex surface directed toward the object side, and abiconvex positive lens L6. Here, the negative meniscus lens L5 and thebiconvex positive lens L6 are cemented.

The third lens unit G3 includes a biconcave negative lens L7. Acyclo-olefin polymer (specific gravity: 1.019 g/cm³) is used for thebiconcave negative lens L7.

The fourth lens unit G4 includes a biconvex positive lens L8.

At the time of zooming from a wide angle end to a telephoto end, thefirst lens unit G1, after moving toward an image side, moves toward theobject side. The second lens unit G2 moves toward the object side. Thethird lens unit G3 moves toward the object side. The fourth lens unit G4is fixed (is stationary). The aperture stop S moves toward the objectside together with the second lens unit G2.

At the time of focusing, the third lens unit G3 moves along an opticalaxis.

An aspheric surface is provided to a total of seven surfaces namely,both surfaces of the positive meniscus lens L4, an image-side surface ofthe biconvex positive lens L6, both surfaces of the biconcave negativelens L7, and both surfaces of the biconvex positive lens L8.

The zoom lens according to the example 2, as shown in FIG. 2A, FIG. 2B,and FIG. 2C, includes in order from an object side, a first lens unit G1having a negative refractive power, a second lens unit G2 having apositive refractive power, a third lens unit G3 having a negativerefractive power, and a fourth lens unit G4 having a positive refractivepower. An aperture stop (stop) S is disposed in the second lens unit G2.

The first lens unit G1 includes a negative meniscus lens L1 having aconvex surface directed toward the object side, a biconcave negativelens L2, and a positive meniscus lens L3 having a convex surfacedirected toward the object side.

The second lens unit G2 includes a positive meniscus lens L4 having aconvex surface directed toward the object side, a negative meniscus lensL5 having a convex surface directed toward the object side, and abiconvex positive lens L6. Here, the negative meniscus lens L5 and thebiconvex positive lens L6 are cemented.

The third lens unit G3 includes a biconcave negative lens L7. Acyclo-olefin polymer (specific gravity: 1.019 g/cm³) is used for thebiconcave negative lens L7.

The fourth lens unit G4 includes a positive meniscus lens L8 having aconvex surface directed toward an image side.

At the time of zooming from a wide angle end to a telephoto end, thefirst lens unit G1, after moving toward an image side, moves toward theobject side. The second lens unit G2 moves toward the object side. Thethird lens unit G3 moves toward the object side. The fourth lens unit G4is fixed (is stationary). The aperture stop S moves toward the objectside together with the second lens unit G2.

At the time of focusing, the third lens unit G3 moves along an opticalaxis.

An aspheric surface is provided to a total of nine surfaces namely, bothsurfaces of the positive meniscus lens L3, both surfaces of the positivemeniscus lens L4, an image-side surface of the biconvex positive lensL6, both surfaces of the biconcave negative lens L7, and both surfacesof the positive meniscus lens L8.

The zoom lens according to the example 3, as shown in FIG. 3A, FIG. 3B,and FIG. 3C, includes in order from an object side, a first lens unit G1having a negative refractive power, a second lens unit G2 having apositive refractive power, a third lens unit G3 having a negativerefractive power, and a fourth lens unit G4 having a positive refractivepower. An aperture stop (stop) is disposed in the second lens unit G2.Moreover, a flair aperture SF is disposed nearest to an image side ofthe second lens unit G2.

The first lens unit G1 includes a negative meniscus lens L1 having aconvex surface directed toward the object side, a biconcave negativelens L2, and a positive meniscus lens L3 having a convex surfacedirected toward the object side.

The second lens unit G2 includes a biconvex positive lens L4, a negativemeniscus lens L5 having a convex surface directed toward the objectside, and a biconvex positive lens L6. Here, the negative meniscus lensL5 and the biconvex positive lens L6 are cemented.

The third lens unit G3 includes a biconcave negative lens L7. Acyclo-olefin polymer (specific gravity: 1.019 g/cm³) is used for thebiconcave negative lens L7.

The fourth lens unit G4 includes a biconvex positive lens L8.

At the time of zooming from a wide angle end to a telephoto end, thefirst lens unit G1, after moving toward the image side, moves toward theobject side. The second lens unit G2 moves toward the object side. Thethird lens unit G3 moves toward the object side. The fourth lens unit G4is fixed (is stationary). The aperture stop (stop) S moves toward theobject side together with the second lens unit G2.

At the time of focusing, the third lens unit G3 moves along an opticalaxis.

An aspheric surface is provided to a total of eight surfaces namely,both surfaces of the biconcave negative lens L2, both surfaces of thepositive meniscus lens L3, both surfaces of the biconvex positive lensL4, and both surfaces of the biconcave negative lens L7.

The zoom lens according to the example 4, as shown in FIG. 4A, FIG. 4B,and FIG. 4C, includes in order from an object side, a first lens unit G1having a negative refractive power, a second lens unit G2 having apositive refractive power, a third lens unit G3 having a negativerefractive power, and a fourth lens unit G4 having a positive refractivepower. An aperture stop (stop) S is disposed in the second lens unit G2.

The first lens unit G1 includes a negative meniscus lens L1 having aconvex surface directed toward the object side, a biconcave negativelens L2, and a positive meniscus lens L3 having a convex surfacedirected toward the object side.

The second lens unit G2 includes a biconvex positive lens L4, a negativemeniscus lens L5 having a convex surface directed toward the objectside, and a biconvex positive lens L6. Here, the negative meniscus lensL5 and the biconvex positive lens L6 are cemented.

The third lens unit G3 includes a negative meniscus lens L7 having aconvex surface directed toward the object side. A cyclo-olefin polymer(specific gravity: 1.019 g/cm³) is used for the negative meniscus lensL7.

The fourth lens unit G4 includes a positive meniscus lens L8 having aconvex surface directed toward an image side.

At the time of zooming from a wide angle end to a telephoto end, thefirst lens unit G1, after moving toward the image side, moves toward theobject side. The second lens unit G2 moves toward the object side. Thethird lens unit G3 moves toward the object side. The fourth lens unit G4is fixed (is stationary). The aperture stop (stop) S moves toward theobject side together with the second lens unit G2.

At the time of focusing, the third lens unit G3 moves along an opticalaxis.

An aspheric surface is provided to a total of six surfaces namely, bothsurfaces of the biconcave negative lens L2, both surfaces of thebiconvex positive lens L4, and both surfaces of the negative meniscuslens L7.

The zoom lens according to the example 5, as shown in FIG. 5A, FIG. 5B,and FIG. 5C, includes in order from an object side, a first lens unit G1having a negative refractive power, a second lens unit G2 having apositive refractive power, a third lens unit G3 having a negativerefractive power, and a fourth lens unit G4 having a positive refractivepower. An aperture stop (stop) S is disposed in the second lens unit G2.

The first lens unit G1 includes a biconcave negative lens L1 and apositive meniscus lens L2 having a convex surface directed toward theobject side.

The second lens unit G2 includes a positive meniscus lens L3 having aconvex surface directed toward the object side, a negative meniscus lensL4 having a convex surface directed toward the object side, and apositive meniscus lens L5 having a convex surface directed toward theobject side. Here, the negative meniscus lens L4 and the positivemeniscus lens L5 are cemented.

The third lens unit G3 includes a negative meniscus lens L6 having aconvex surface directed toward the object side. A cyclo-olefin polymer(specific gravity: 1.019 g/cm³) is used for the negative meniscus lensL6.

The fourth lens unit G4 includes a biconvex positive lens L7.

At the time of zooming from a wide angle end to a telephoto end, thefirst lens unit G1, after moving toward an image side, moves toward theobject side. The second lens unit G2 moves toward the object side. Thethird lens unit G3 moves toward the object side. The fourth lens unit G4is fixed (is stationary). The aperture stop (stop) S moves toward theobject side together with the second lens unit G2.

At the time of focusing, the third lens unit G3 moves along an opticalaxis.

An aspheric surface is provided to a total of 11 surfaces namely, bothsurfaces of the biconcave negative lens L1, both surfaces of thepositive meniscus lens L2, both surfaces of the positive meniscus lensL3, an image-side surface of the positive meniscus lens L5, bothsurfaces of the negative meniscus lens L6, and both surfaces of thebiconvex positive lens L7.

Numerical data of each example described above is shown below. Apartfrom symbols described above, r denotes radius of curvature of each lenssurface, d denotes a distance between respective lens surfaces, nddenotes a refractive index of each lens for a d-line, νd denotes an Abbenumber for each lens and * denotes an aspheric surface. Further, fdenotes a focal length of the entire system, FNO. denotes an F number, ωdenotes a half angle of view, IH denotes an image height, FB denotes aback focus, Lens total length is a distance from a lens forefrontsurface up to a lens backmost surface (without air conversion) and eachof f1, f2 . . . is a focal length of each lens unit. Further, FB (backfocus) is a unit which is expressed upon air conversion of a distancefrom the lens backmost surface to a paraxial image surface. Further, WEdenotes a wide angle end, ST denotes a intermediate focal length state,TE denotes a telephoto end.

A shape of an aspheric surface is defined by the following expressionwhere the direction of the optical axis is represented by z, thedirection orthogonal to the optical axis is represented by y, a conicalcoefficient is represented by K, aspheric surface coefficients arerepresented by A4, A6, A8, A10,Z=(y ² /r)/[1+{1−(1+k)(y/r)²}^(1/2) ]+A4y ⁴ +A6y ⁶ +A8y ⁸ +A10y ¹⁰ +A12y¹²

Further, in the aspherical surface coefficients, ‘e−n’ (where, n is anintegral number) indicates ‘10^(−n)’. Moreover, these symbols arecommonly used in the following numerical data for each example.

EXAMPLE 1

Unit mm Surface data Surface no. r d nd νd Object plane ∞ ∞  1 33.5010.800 1.77250 49.60  2 11.209 4.041  3 −45.096 0.700 1.49700 81.54  423.551 0.289  5 16.607 1.820 2.00100 29.13  6 30.330 Variable  7* 10.8612.248 1.80139 45.45  8* 234.877 0.539  9(Stop) ∞ 1.100 10 903.915 0.4001.66680 33.05 11 7.093 3.523 1.49700 81.54 12* −19.000 Variable 13*−36.032 0.600 1.53071 55.69 14* 19.120 Variable 15* 681.183 4.2791.53071 55.69 16* −19.776 14.218 Image plane ∞ Aspherical surface data7th surface k = 0.0000 A4 = 5.7968e−005, A6 = 5.3399e−007, A8 =4.2448e−008, A10 = 3.5914e−010, A12 = 1.8404e−012 8th surface k = 0.0000A4 = 1.7402e−004, A6 = −1.2118e−006, A8 = 1.1537e−007, A10 =−8.4375e−010, A12 = −2.0822e−011 12th surface k = 0.0000 A4 =6.3514e−005, A6 = 8.6302e−006, A8 = −4.8301e−007, A10 = 1.7306e−008, A12= −2.6091e−011 13th surface k = 0.0000 A4 = 1.3252e−003, A6 =−3.5798e−005, A8 = −6.7078e−007, A10 = 4.2140e−008, A12 = 1.1014e−01014th surface k = 0.0000 A4 = 1.4150e−003, A6 = −3.2179e−005, A8 =−7.7489e−007, A10 = 4.2602e−008, A12 = −2.5783e−011 15th surface k =0.0000 A4 = −7.3221e−005, A6 = 1.8445e−006, A8 = −8.7997e−009, A10 =−2.8574e−011, A12 = 2.2692e−013 16th surface k = 0.0000 A4 =−4.0767e−005, A6 = 5.4018e−008, A8 = 1.9184e−008, A10 = −2.0974e−010,A12 = 6.4768e−013 Zoom data WE ST TE f 14.240 24.250 41.180 Fno. 3.5964.418 5.802 2ω 82.4 49.4 29.9 IH 11.15 11.15 11.15 FB 14.218 14.21814.218 Lens total length 48.919 44.885 47.867 d6 18.700 7.466 0.500 d122.031 5.615 11.656 d14 7.849 11.465 15.372 Unit focal length f1 =−19.884 f2 = 14.338 f3 = −23.449 f4 = 36.289

EXAMPLE 2

Unit mm Surface data Surface no. r d nd νd Object plane ∞ ∞  1 64.7020.800 1.69680 55.53  2 11.606 3.422  3 −88.327 0.700 1.49700 81.54  427.506 0.200  5* 15.778 1.914 1.63493 23.90  6* 31.865 Variable  7*10.795 2.116 1.80139 45.45  8* 113.014 0.849  9(Stop) ∞ 1.000 10 28.8170.400 1.90366 31.32 11 7.100 3.500 1.59201 67.02 12* −24.966 Variable13* −171.145 0.600 1.53071 55.69 14* 11.052 Variable 15* −97.090 3.5741.76802 49.24 16* −20.177 14.438 Image plane ∞ Aspherical surface data5th surface k = 0.0000 A4 = −8.1884e−005, A6 = −2.7042e−007, A8 =1.4238e−008, A10 = −4.0588e−010 6th surface k = 0.0000 A4 =−9.9349e−005, A6 = 4.2182e−007, A8 = −6.1084e−009, A10 = −2.2166e−0107th surface k = 0.0000 A4 = 4.2062e−005, A6 = −5.7246e−007, A8 =7.1083e−008, A10 = −1.2063e−009 8th surface k = 0.0000 A4 = 1.6242e−004,A6 = −1.7979e−006, A8 = 1.0048e−007, A10 = −2.0625e−009 12th surface k =0.0000 A4 = 3.4943e−005, A6 = 2.8257e−006, A8 = −7.7626e−008, A10 =4.2720e−009 13th surface k = 0.0000 A4 = 5.1140e−004, A6 = −3.3672e−005,A8 = 1.0216e−006, A10 = −1.3810e−008 14th surface k = 0.0000 A4 =5.7630e−004, A6 = −3.2837e−005, A8 = 8.6468e−007, A10 = −1.0733e−00815th surface k = 0.0000 A4 = −3.8824e−005, A6 = 7.4513e−007, A8 =−2.1479e−009, A10 = −1.0307e−011 16th surface k = 0.0000 A4 =−2.5322e−005, A6 = 2.0336e−007, A8 = 3.7625e−009, A10 = −2.9594e−011Zoom data WE ST TE f 14.240 24.250 41.180 Fno. 3.599 4.422 5.731 2ω 82.449.2 29.4 IH 11.15 11.15 11.15 FB 14.438 14.438 14.438 Lens total length46.746 44.301 46.603 d6 17.597 7.338 0.500 d12 2.235 5.330 11.119 d147.839 12.558 15.909 Unit focal length f1 = −18.802 f2 = 13.533 f3 =−19.540 f4 = 32.507

EXAMPLE 3

Unit mm Surface data Surface no. r d nd νd Object plane ∞ ∞  1 26.7560.500 1.80400 46.57  2 9.825 3.870  3* −59.361 0.600 1.53071 55.69  4*20.071 0.344  5* 12.459 2.108 1.63493 23.90  6* 33.129 Variable  7*11.351 2.578 1.80610 40.88  8* −73.783 1.000  9(Stop) ∞ 0.961 10 54.9840.519 1.80000 29.84 11 6.363 3.937 1.49700 81.54 12 −18.990 0.00013(Stop) ∞ Variable 14* −38.199 0.525 1.53071 55.69 15* 13.061 Variable16 72.188 3.692 1.76200 40.10 17 −35.038 14.481 Image plane ∞ Asphericalsurface data 3rd surface k = 0.0000 A4 = 6.6345e−005, A6 = −5.0207e−007,A8 = 2.1595e−009 4th surface k = 0.0000 A4 = −2.2600e−005 5th surface k= 0.0000 A4 = −8.7714e−005 6th surface k = 0.0000 A4 = 4.8290e−006, A6 =−4.7938e−007, A8 = 2.6845e−009 7th surface k = 0.0000 A4 = −3.2000e−005,A6 = −3.6289e−007, A8 = −3.0000e−009 8th surface k = 0.0000 A4 =7.2057e−005, A6 = −4.5933e−007 14th surface k = 0.0000 A4 = 2.8473e−005,A6 = 2.1654e−006 15th surface k = 0.0000 A4 = 5.6057e−005, A6 =4.7498e−007, A8 = −1.1679e−008 Zoom data WE ST TE f 14.233 24.250 41.282Fno. 3.640 4.518 5.738 2ω 82.4 49.5 29.1 IH 11.15 11.15 11.15 FB 14.48114.481 14.481 Lens total length 48.096 46.306 48.308 d6 17.971 7.7490.700 d13 1.857 5.158 11.607 d15 7.634 12.765 15.367 Unit focal lengthf1 = −18.194 f2 = 13.826 f3 = −18.275 f4 = 31.424

EXAMPLE 4

Unit mm Surface data Surface no. r d nd νd Object plane ∞ ∞  1 44.8460.500 1.77250 49.60  2 10.080 4.150  3* −40.189 0.760 1.53071 55.69  4*38.530 0.190  5 17.821 1.700 2.00069 25.46  6 37.691 Variable  7* 12.1472.711 1.74156 49.21  8* −62.740 1.000  9(Stop) ∞ 1.120 10 136.852 0.5201.74951 35.33 11 6.962 4.200 1.49700 81.54 12 −15.588 Variable 13*47.328 0.400 1.53071 55.69 14* 10.352 Variable 15 −99.929 2.300 1.8348142.73 16 −26.850 15.335 Image plane ∞ Aspherical surface data 3rdsurface k = 0.0000 A4 = 6.6785e−005, A6 = −8.8705e−007, A8 =−9.6050e−010, A10 = −8.1513e−013 4th surface k = 0.0000 A4 =5.6775e−005, A6 = −1.1574e−006, A8 = −1.5695e−011 7th surface k = 0.0000A4 = −2.4426e−005, A6 = −3.5991e−007, A8 = 1.4222e−008, A10 =−7.5500e−010 8th surface k = 0.0000 A4 = 8.7510e−005, A6 = −3.4669e−007,A8 = 3.1047e−010, A10 = −5.2955e−010 13th surface k = 0.0000 A4 =−4.2631e−004, A6 = 8.4142e−006, A8 = 8.5933e−008, A10 = −1.9000e−00914th surface k = 0.0000 A4 = −4.7992e−004, A6 = 9.9258e−006, A8 =−5.6689e−008 Zoom data WE ST TE f 14.323 24.252 41.582 Fno. 3.645 4.6975.798 2ω 83.7 49.5 29.2 IH 11.15 11.15 11.15 FB 15.334 15.334 15.334Lens total length 48.921 45.522 50.145 d6 17.997 7.188 0.500 d12 1.2685.104 11.309 d14 10.105 13.679 18.785 Unit focal length f1 = −18.140 f2= 14.653 f3 = −25.060 f4 = 43.359

EXAMPLE 5

Unit mm Surface data Surface no. r d nd νd Object plane ∞ ∞  1* −461.3930.800 1.86400 40.58  2* 11.063 2.637  3* 18.993 2.251 1.92286 20.88  4*46.130 Variable  5* 11.342 1.969 1.75501 51.16  6* 81.309 1.264  7(Stop)∞ 2.052  8 24.185 0.400 1.66680 33.05  9 6.053 3.389 1.55332 71.68 10*200.000 Variable 11* 282.863 0.500 1.53071 55.69 12* 13.402 Variable 13*156.989 3.483 1.76802 49.24 14* −29.889 14.059 Image plane ∞ Asphericalsurface data 1st surface k = 0.0000 A4 = 1.3367e−005, A6 = −2.5655e−007,A8 = 8.0868e−010 2nd surface k = 0.0000 A4 = −4.4507e−005, A6 =−2.7242e−007, A8 = −7.2137e−009 3rd surface k = 0.0000 A4 = −4.9213e−0054th surface k = 0.0000 A4 = −5.7000e−005 5th surface k = 0.0000 A4 =−2.2138e−005 6th surface k = 0.0000 A4 = 3.7409e−006, A6 = 2.5909e−00810th surface k = 0.0000 A4 = 1.8000e−004, A6 = 2.1105e−006, A8 =−7.0000e−009 11th surface k = 0.0000 A4 = −4.7516e−006, A6 =−9.9206e−006, A8 = 5.1820e−007, A10 = −9.8198e−009 12th surface k =0.0000 A4 = −4.9496e−007, A6 = −6.6995e−006, A8 = 2.9424e−007, A10 =−5.4932e−009 13th surface k = 0.0000 A4 = −2.0000e−005, A6 =8.4626e−008, A8 = 3.4000e−009, A10 = −3.6422e−011 14th surface k =0.0000 A4 = −1.1571e−005, A6 = −2.7433e−007, A8 = 7.3343e−009, A10 =−4.8697e−011 Zoom data WE ST TE f 14.370 24.361 41.394 Fno. 3.707 4.4835.828 2ω 83.1 48.9 29.2 IH 11.15 11.15 11.15 FB 14.058 14.058 14.058Lens total length 47.521 43.230 47.605 d4 19.793 8.008 0.908 d10 1.8316.211 13.087 d12 7.152 10.266 14.865 Unit focal length f1 = −21.792 f2 =15.820 f3 = −26.526 f4 = 32.960

Aberration diagrams of the examples from the example 1 to example 5 areshown in diagrams from FIG. 6A, FIG. 6B, FIG. 6C, FIG. 6D, FIG. 6E, FIG.6F, FIG. 6G, FIG. 6H, FIG. 6I, FIG. 6J, FIG. 6K, and FIG. 6L to FIG.10A, FIG. 10B, FIG. 10C, FIG. 10D, FIG. 10E, FIG. 10F, FIG. 10G, FIG.10H, FIG. 10I, FIG. 10J, FIG. 10K, and FIG. 10L. Each of the aberrationdiagrams is an aberration diagram when focused to an object at infinity.Moreover, in each diagram ‘FIY’ indicates the maximum image height.

In the aberration diagrams, diagrams from FIG. 6A, FIG. 7A, FIG. 8A,FIG. 9A, and FIG. 10A to FIG. 6D, FIG. 7D, FIG. 8D, FIG. 9D, and FIG.10D are diagrams at a wide angle end. FIG. 6A, FIG. 7A, FIG. 8A, FIG.9A, and FIG. 10A show a spherical aberration (SA), FIG. 6B, FIG. 7B,FIG. 8B, FIG. 9B, and FIG. 10B show an astigmatism (AS), FIG. 6C, FIG.7C, FIG. 8C, FIG. 9C, and FIG. 10C show a distortion (DT), and FIG. 6D,FIG. 7D, FIG. 8D, FIG. 9D, and FIG. 10D show a chromatic aberration ofmagnification (CC).

Moreover, diagrams from FIG. 6E, FIG. 7E, FIG. 8E, FIG. 9E, and FIG. 10Eto FIG. 6H, FIG. 7H, FIG. 8H, FIG. 9H, and FIG. 10H are aberrationdiagrams in an intermediate focal length state. FIG. 6E, FIG. 7E, FIG.8E, FIG. 9E, and FIG. 10E show a spherical aberration (SA), FIG. 6F,FIG. 7F, FIG. 8F, FIG. 9F, and FIG. 10F show an astigmatism (AS), FIG.6G, FIG. 7G, FIG. 8G, FIG. 9G, and FIG. 10G show a distortion (DT), andFIG. 6H, FIG. 7H, FIG. 8H, FIG. 9H, and FIG. 10H show a chromaticaberration of magnification (CC).

Furthermore, diagrams from FIG. 6I, FIG. 7I, FIG. 8I, FIG. 9I, and FIG.10I to FIG. 6L, FIG. 7L, FIG. 8L, FIG. 9L, and FIG. 10L are aberrationdiagrams at a telephoto end. FIG. 6I, FIG. 7I, FIG. 8I, FIG. 9I, andFIG. 10I show a spherical aberration (SA), FIG. 6J, FIG. 7J, FIG. 8J,FIG. 9J, and FIG. 10J show an astigmatism (AS), FIG. 6K, FIG. 7K, FIG.8K, FIG. 9K, and FIG. 10K show a distortion (DT), and FIG. 6L, FIG. 7L,FIG. 8L, FIG. 9L, and FIG. 10L show a chromatic aberration ofmagnification (CC).

Next, values of conditional expressions (1) to (24) in each example aregiven below. Specific gravity is a value for the negative lens in thethird lens unit. Moreover, ‘-’ (hyphen) indicates that there is noarrangement for calculating the value.

Exam- Exam- Exam- Exam- Exam- ple 1 ple 2 ple 3 ple 4 ple 5 (1)ΔD₁₂/ER_(S) 4.09 3.758 3.675 3.637 4.197 (2) |f₃/f_(UN21)| 1.658 1.3241.477 1.798 1.538 (3) SF_(2N) 0.31 0.53 0.49 0.02 — (4) ΔD₁₂/IH_(MAX)1.632 1.533 1.549 1.569 1.694 (5) |f₃/f_(W)| 1.647 1.372 1.284 1.751.846 (6) Σ_(2G)/f₂ 0.54 0.58 0.65 0.65 0.57 (7) f_(UN21)/f₂ 0.987 1.090.895 0.951 1.09 (8) |f₃/f₂| 1.64 1.44 1.32 1.71 1.68 (9) f₂/IH_(MAX)1.29 1.21 1.24 1.31 1.42 (10) f_(UN21)/ER_(S) 3.179 3.243 2.632 2.8973.833 (11) LTL_(min)/fb_(LTLmin) 4.157 4.068 4.198 3.969 4.075 (12)DT_(W) −10.56 −10.56 −10.51 −13.09 −12.45 (13) SF_(UN21) −1.1 −1.21−0.73 −0.68 −1.32 (14) Σ_(2G)/f_(W) 0.55 0.55 0.63 0.67 0.63 (15)|f₃/IH_(MAX)| 2.1 1.75 1.64 2.25 2.38 (16) ν_(p1) 81.54 67.02 81.5481.54 71.68 (17) fb_(w)/IH_(MAX) 1.28 1.29 1.3 1.38 1.26 (18) f₁/f₃ 0.850.96 1 0.72 0.82 (19) LTL_(w)/fb_(w) 4.44 4.24 4.32 4.19 4.38 (20)f_(UN21)/f_(W) 0.993 1.036 0.869 0.973 1.2 (21) ΔD₁₂/f_(T) 0.442 0.4150.418 0.421 0.456 (22) |f₃/ER_(S)| 0.756 0.464 0.648 0.678 0.788 (23)|ASP_(O) − ASP_(I)|/ — 0.0014 0.0006 0.0057 — IH_(33W) (24) f_(T)/f_(W)2.89 2.89 2.90 2.90 2.88 specific gravity(g/cm³) 1.01 1.01 1.01 1.011.01

FIG. 13 is a cross-sectional view of an interchangeable lens camera asan electronic image pickup apparatus. The interchangeable lens camera isa single-lens mirrorless camera which is a camera of the type not tohave a quick return mirror, for example. In FIG. 13, a taking opticalsystem. 2 is disposed inside a lens barrel of a single-lens mirrorlesscamera 1. A mount portion 3 enables the taking optical system 2 to bedetachable from a body of the single-lens mirrorless camera 1. As themount portion 3, a mount such as a screw-type mount and a bayonet-typemount is to be used. In this example, a bayonet-type mount is used.Moreover, an image pickup element surface 4 and a back monitor 5 aredisposed in the body of the single-lens mirrorless camera 1. As an imagepickup element, an element such as a small-size CCD (charge coupleddevice) or a CMOS (complementary metal-oxide semiconductor) is to beused.

Moreover, as the taking optical system 2 of the single-lens mirrorlesscamera 1, the zoom lens described in any one of the examples from thefirst example to the fifth example is to be used.

FIG. 14 and FIG. 15 are conceptual diagrams of an arrangement of theimage pickup apparatus which has the zoom lens according to the presentexample. FIG. 14 is a front perspective view showing an appearance of asingle-lens mirrorless camera 40 as the image pickup apparatus, and FIG.15 is a rear perspective view of the single-lens mirrorless camera 40.The zoom lens according to the present example is used in a photographicoptical system 41 of the single-lens mirrorless camera 40.

The single-lens mirrorless camera 40 according to the present embodimentincludes the photographic optical system 41 which is positioned in aphotographic optical path 42, a shutter button 45, and a liquid-crystaldisplay monitor 47. As the shutter button 45 disposed on an upperportion of the single-lens mirrorless camera 40 is pressed, inconjunction with the pressing of the shutter button 45, photography iscarried out by the photographic optical system 41 such as the zoom lensaccording to the first example. An object image which is formed by thephotographic optical system 41 is formed on an image pickup element(photoelectric conversion surface) which is provided near an imageforming surface. The object image which has been received optically bythe image pickup element is displayed on the liquid-crystal displaymonitor 47 which is provided to a rear surface of the camera, as anelectronic image by a processing means. Moreover, it is possible torecord the electronic image which has been photographed, in a recordingmeans.

FIG. 16 is a structural block diagram of an internal circuit of maincomponents of the single-lens mirrorless camera 40. In the followingdescription, the processing means described above includes for instance,a CDS/ADC section 24, a temporary storage memory 17, and an imageprocessing section 18, and a storage means consists of a storage mediumsection 19 for example.

As shown in FIG. 16, the single-lens mirrorless camera 40 includes anoperating section 12, a control section 13 which is connected to theoperating section 12, the temporary storage memory 17 and an imagingdrive circuit 16 which are connected to a control-signal output port ofthe control section 13, via a bus 14 and a bus 15, the image processingsection 18, the storage medium section 19, a display section 20, and aset-information storage memory section 21.

The temporary storage memory 17, the image processing section 18, thestorage medium section 19, the display section 20, and theset-information storage memory section 21 are structured to be capableof mutually inputting and outputting data via a bus 22. Moreover, theCCD 49 and the CDS/ADC section 24 are connected to the imaging drivecircuit 16.

The operating section 12 includes various input buttons and switches,and informs the control section 13 of event information which is inputfrom outside (by a user of the digital camera) via these input buttonsand switches. The control section 13 is a central processing unit (CPU),and has a built-in computer program memory which is not shown in thediagram. The control section 13 controls the entire single-lensmirrorless camera 40 according to a computer program stored in thiscomputer program memory.

The CCD 49 is driven and controlled by the imaging drive circuit 16, andwhich converts an amount of light for each pixel of the object imagewhich formed through the photographic optical system 41 to an electricsignal, and outputs to the CDS/ADC section 24.

The CDS/ADC section 24 is a circuit which amplifies the electric signalwhich is input from the CCD 49, and carries out analog/digitalconversion, and outputs to the temporary storage memory 17 image rawdata (Bayer data, hereinafter called as ‘RAW data’) which is onlyamplified and converted to digital data.

The temporary storage memory 17 is a buffer which includes an SDRAM(Synchronous Dynamic Random Access Memory) for example, and is a memorydevice which stores temporarily the RAW data which is output from theCDS/ADC section 24. The image processing section 18 is a circuit whichreads the RAW data stored in the temporary storage memory 17, or the RAWdata stored in the storage medium section 19, and carries outelectrically various image-processing including the distortioncorrection, based on image-quality parameters specified by the controlsection 13.

The storage medium section 19 is a recording medium in the form of acard or a stick including a flash memory for instance, detachablymounted. The storage medium section 19 records and maintains the RAWdata transferred from the temporary storage memory 17 and image datasubjected to image processing in the image processing section 18 in thecard flash memory and the stick flash memory.

The display section 20 includes the liquid-crystal display monitor, anddisplays images and operation menu on the liquid-crystal displaymonitor. The set-information storage memory section 21 includes a ROMsection in which various image quality parameters are stored in advance,and a RAM section which stores image quality parameters which areselected by an input operation on the operating section 12, from amongthe image quality parameters which are read from the ROM section.

The single-lens mirrorless camera 40 structured in such manner can be animage pickup apparatus having a zoom lens in which, both favorablecorrection of various aberrations and small-sizing. Moreover, the zoomlens according to the present invention can be used for an image pickupapparatus of the type which optical system is fixed to a body of theimage pickup apparatus.

According to the present invention, it is possible to provide a zoomlens in which, both favorable correction of various aberrations andsmall-sizing of the optical system are achieved, and an image pickupapparatus using such zoom lens.

As it has been described so far, the present invention is suitable for azoom lens in which, both favorable correction of various aberrations andsmall-sizing of the optical system are achieved, and the image pickupapparatus using such zoom lens.

What is claimed is:
 1. A zoom lens comprising in order from an objectside to an image side: a first lens unit having a negative refractivepower; a second lens unit having a positive refractive power; and athird lens unit having a negative refractive power, wherein at the timeof zooming, distances between the lens units change, and a distancebetween the first lens unit and the second lens unit at a telephoto endis shorter than a distance between the first lens unit and the secondlens unit at a wide angle end, and an aperture stop is disposed on theimage side of an image-side surface of the first lens unit, and on theobject side of an image-side surface of the second lens unit, and thesecond lens unit includes in order from the object side to the imageside, an object-side sub lens unit having a positive refractive powerand an image-side sub lens unit, and the object-side sub lens unit inthe second lens unit includes one lens component, and in the lenscomponent, only an object-side surface and an image-side surface are incontact with air in an optical path, and the following conditionalexpressions (1) and (2) are satisfied3.0<ΔD ₁₂ /ER _(S)<4.5  (1)1.05<|f ₃ /f _(UN21)|<2.1  (2) where,ΔD ₁₂ =D _(12W) −D _(12T), D_(12w) denotes the distance between thefirst lens unit and the second lens unit at the wide angle end, D_(12T)denotes the distance between the first lens unit and the second lensunit at the telephoto end, both D_(12W) and D_(12T) are distances on anoptical axis at the time of infinite object point focusing, ER_(S)denotes the maximum radius of an opening of the aperture stop, f₃denotes a focal length of the third lens unit, and f_(UN21) denotes afocal length of the object-side sub lens unit in the second lens unit.2. A zoom lens comprising in order from an object side to an image side:a first lens unit having a negative refractive power; a second lens unithaving a positive refractive power; and a third lens unit having anegative refractive power, wherein at the time of zooming, distancesbetween the lens units change, and a distance between the first lensunit and the second lens unit at a telephoto end is shorter than adistance between the first lens unit and the second lens unit at a wideangle end, and an aperture stop is disposed on the image side of animage-side surface of the first lens unit, and on the object side of animage-side surface of the second lens unit, and the first lens unitincludes in order from the object side to the image side, an object-sidesub lens unit and an image-side sub lens unit, and the object-side sublens unit in the first lens unit includes a first negative lens, and theimage-side sub lens unit in the first lens unit includes a secondnegative lens and a first positive lens, and the second lens unitincludes in order from the object side to the image side, an object-sidesub lens unit having a positive refractive power, and an image-side sublens unit, and the object-side sub lens unit in the second lens unitincludes one lens component, and in the lens component, only anobject-side surface and an image-side surface are in contact with air inan optical path, and the following conditional expressions (1) and (3)are satisfied3.0<ΔD ₁₂ /ER _(S)<4.5  (1)−0.9<SF _(2N)<1.5  (3) where,ΔD ₁₂ =D _(12W) −D _(12T), D_(12W) denotes the distance between thefirst lens unit and the second lens unit at the wide angle end, D_(12T)denotes the distance between the first lens unit and the second lensunit at the telephoto end, both D_(12W) and D_(12T) are distances on anoptical axis at the time of infinite object point focusing, ER_(S)denotes the maximum radius of an opening of the aperture stop,SF _(2N)=(R _(2NO) +R _(2NI))/(R _(2NO) −R _(2NI)), R_(2NO) denotes aparaxial radius of curvature of an object-side surface of the secondnegative lens in the first lens unit, and R_(2NI) denotes a paraxialradius of curvature of an image-side surface of the second negative lensin the first lens unit.
 3. A zoom lens comprising in order from anobject side to an image side: a first lens unit having a negativerefractive power; a second lens unit having a positive refractive power;and a third lens unit having a negative refractive power, wherein at thetime of zooming, distances between the lens units change, and a distancebetween the first lens unit and the second lens unit at a telephoto endis shorter than a distance between the first lens unit and the secondlens unit at a wide angle end, and an aperture stop is disposed on theimage side of an image-side surface of the first lens unit, and on theobject side of an image-side surface of the second lens unit, and thesecond lens unit includes in order from the object side to the imageside, an object-side sub lens unit having a positive refractive powerand an image-side sub lens unit, and the object-side sub lens unit inthe second lens unit includes one lens component, and in the lenscomponent, only an object-side surface and an image-side surface are incontact with air in an optical path, and the following conditionalexpressions (2′), (4), (5′) and (8′) are satisfied1.2<|f ₃ /f _(UN21)|<2.1  (2′)1.2<ΔD ₁₂ /IH _(MAX)<1.85  (4)1.1<|f ₃ /f _(W)|<1.9  (5′)1.3<|f ₃ /f ₂|<1.95  (8′) where,ΔD ₁₂ =D _(12W) −D _(12T), D_(12W) denotes the distance between thefirst lens unit and the second lens unit at the wide angle end, D_(12T)denotes the distance between the first lens unit and the second lensunit at the telephoto end, both D_(12W) and D_(12T) are distances on anoptical axis at the time of infinite object point focusing, IH_(MAX)denotes the maximum image height, and denotes the maximum value in acase in which, the maximum image height changes with zooming, f₃ denotesa focal length of the third lens unit, f_(W) denotes a focal length ofthe overall zoom lens system at the time of infinite object pointfocusing at the wide angle end, f₂ denotes a focal length of the secondlens unit, and f_(UN21) denotes a focal length of the object-side sublens unit in the second lens unit.
 4. A zoom lens comprising in orderfrom an object side to an image side: a first lens unit having anegative refractive power; a second lens unit having a positiverefractive power; and a third lens unit having a negative refractivepower, wherein at the time of zooming, distances between the lens unitschange, and a distance between the first lens unit and the second lensunit at a telephoto end is shorter than a distance between the firstlens unit and the second lens unit at a wide angle end, and an aperturestop is disposed on the image side of an image-side surface of the firstlens unit, and on the object side of an image-side surface of the secondlens unit, and the following conditional expressions (4) and (6) aresatisfied1.2<ΔD ₁₂ /IH _(MAX)<1.85  (4)0.43<Σ_(2G) /f ₂<0.78  (6) where,ΔD ₁₂ =D _(12W) −D _(12T), D_(12W) denotes the distance between thefirst lens unit and the second lens unit at the wide angle end, D_(12T)denotes the distance between the first lens unit and the second lensunit at the telephoto end, both D_(12W) and _(D12T) are distances on anoptical axis at the time of infinite object point focusing, IH_(MAX)denotes the maximum image height, and denotes the maximum value in acase in which, the maximum image height changes with zooming, Σ_(2G)denotes a thickness on an optical axis of the second lens unit, and f₂denotes a focal length of the second lens unit.
 5. A zoom lenscomprising in order from an object side to an image side: a first lensunit having a negative refractive power; a second lens unit having apositive refractive power; and a third lens unit having a negativerefractive power, wherein at the time of zooming, distances between thelens units change, and a distance between the first lens unit and thesecond lens unit at a telephoto end is shorter than a distance betweenthe first lens unit and the second lens unit at a wide angle end, and anaperture stop is disposed on the image side of an image-side surface ofthe first lens unit, and on the object side of an image-side surface ofthe second lens unit, and the second lens unit includes in order fromthe object side to the image side, an object-side sub lens unit having apositive refractive power, and an image-side sub lens unit, and theobject-side sub lens unit in the second lens unit includes one lenscomponent, and in the lens component, only an object-side surface and animage-side surface are in contact with air in an optical path, and thefollowing conditional expressions (7), (8′),(9) and (14) are satisfied0.6<f _(UN21) /f ₂<1.8  (7)1.3<|f ₃ /f ₂|<1.95  (8′)1.15<f ₂ / IH _(MAX)<1.5  (9)0.38<Σ_(2G) /f _(W)<0.75  (14) where, f_(UN21) denotes a focal length ofthe object-side sub lens unit in the second lens unit, f₂ denotes afocal length of the second lens unit, f₃ denotes a focal length of thethird lens unit, IH_(MAX) denotes the maximum image height, and denotesthe maximum value in a case in which, the maximum image height changeswith zooming, Σ_(2G) denotes a thickness of the second lens unit on anoptical axis, and f_(W) denotes a focal length of the overall zoom lenssystem at the time of infinite object point focusing at the wide angleend.
 6. A zoom lens comprising in order from an object side to an imageside: a first lens unit having a negative refractive power; a secondlens unit having a positive refractive power; and a third lens unithaving a negative refractive power, wherein at the time of zooming,distances between the lens units change, and a distance between thefirst lens unit and the second lens unit at a telephoto end is shorterthan a distance between the first lens unit and the second lens unit ata wide angle end, and an aperture stop is disposed on the image side ofan image-side surface of the first lens unit, and on the object side ofan image-side surface of the second lens unit, and the first lens unitincludes in order from the object side to the image side, an object-sidesub lens unit and an image-side sub lens unit, and the object-side sublens unit in the first lens unit includes a first negative lens, and theimage-side sub lens unit in the first lens unit includes a secondnegative lens and a first positive lens, and the second lens unitincludes in order from the object side to the image side, an object-sidesub lens unit having a positive refractive power, and an image-side sublens unit, and the object-side sub lens unit in the second lens unitincludes one lens component, and in the lens component, only anobject-side surface and an image-side surface are in contact with air inan optical path, and the image-side sub lens unit in the second lensunit includes a lens surface having a negative refractive power and apositive lens which is disposed on the image side of the lens surface,and the following conditional expressions (3), (10), and (11) aresatisfied−0.9<SF_(2N)<1.5  (3)1.5<f _(UN21) /ER _(S)<3.9  (10)3<LTL _(min) /fb _(LTLmin)<13  (11) where,SF _(2N)=(R _(2NO) +R _(2NI))/(R _(2NO) −R _(2NI)), R_(2NO) denotes aparaxial radius of curvature of an object-side surface of the secondnegative lens in the first lens unit, and R_(2NI) denotes a paraxialradius of curvature of an image-side surface of the second negative lensin the first lens unit, f_(UN21) denotes a focal length of theobject-side sub lens unit in the second lens unit, ER_(S) denotes themaximum radius of an opening of the aperture stop, LTL_(min) denotes asum of an overall length of the zoom lens at the time of infinite objectpoint focusing and an air-converted back focus, and is the minimum valuethereof in a case in which, the overall length changes with zooming, andthe overall length is a distance on an optical axis from a refractingsurface of the zoom lens nearest to the object side and a refractingsurface of the zoom lens nearest to the image side, and fb_(LTLmin)denotes the air-converted back focus at LTL_(min).
 7. A zoom lenscomprising in order from an object side to an image side: a first lensunit having a negative refractive power; a second lens unit having apositive refractive power; and a third lens unit having a negativerefractive power, wherein at the time of zooming, distances between thelens units change, and a distance between the first lens unit and thesecond lens unit at a telephoto end is shorter than a distance betweenthe first lens unit and the second lens unit at a wide angle end, and anaperture stop is disposed on the image side of an image-side surface ofthe first lens unit, and on the object side of an image-side surface ofthe second lens unit, and the second lens unit includes in order fromthe object side to the image side, an object-side sub lens unit having apositive refractive power, and an image-side sub lens unit, and theobject-side sub lens unit in the second lens unit includes one lenscomponent, and in the lens component, only an object-side surface and animage-side surface are in contact with air in an optical path, and thefollowing conditional expressions (2) and (4) are satisfied1.05<|f ₃ /f _(UN21)|<2.1  (2)1.2<ΔD ₁₂ /IH _(MAX)<1.85  (4) where, f₃ denotes a focal length of thethird lens unit, and f_(UN21) denotes a focal length of the object-sidesub lens unit in the second lens unit,ΔD ₁₂ =D _(12W) −D _(12T), D_(12W) denotes the distance between thefirst lens unit and the second lens unit at the wide angle end, D_(12T)denotes the distance between the first lens unit and the second lensunit at the telephoto end, both D_(12W) and D_(12T) are distances on anoptical axis at the time of infinite object point focusing, and IH_(MAX)denotes the maximum image height, and denotes the maximum value in acase in which, the maximum image height changes with zooming.
 8. Thezoom lens according to claim 1, further comprising: a fourth lens unithaving a positive refractive power, disposed on the image side of thethird lens unit, wherein at the time of zooming, a distance between thethird lens unit and the fourth lens unit changes.
 9. The zoom lensaccording to claim 8, wherein a distance between the third lens unit andthe fourth lens unit at the telephoto end is longer than a distancebetween the third lens unit and the fourth lens unit at the wide angleend.
 10. The zoom lens according to claim 8, wherein the total number oflens units in the zoom lens is four, including the first lens unit, thesecond lens unit, the third lens unit, and the fourth lens unit.
 11. Thezoom lens according to claim 1, wherein the object-side sub lens unitand the image-side sub lens unit in the second lens unit are disposedsuch that, an axial air space between the object-side sub lens unit andthe image-side sub lens unit is the maximum in the second lens unit. 12.The zoom lens according to claim 11, wherein the image-side sub lensunit in the second lens unit includes one lens component, and in thelens component, only the object-side surface and the image-side surfaceare in contact with air in the optical path.
 13. The zoom lens accordingto claim 1, wherein the following conditional expression (5) issatisfied0.8<|f ₃ /f _(W)|<2.5  (5) where, f₃ denotes a focal length of the thirdlens unit, and f_(W) denotes a focal length of the overall zoom lenssystem at the time of infinite object point focusing at the wide angleend.
 14. The zoom lens according to claim 1, wherein the followingconditional expression (12) is satisfied−20.0%<DT_(W)<−6.0%  (12) where,DT_(W) ={IH _(W) −f _(W)×tan(ω_(W))}/{f _(W)×tan (ω_(W))}×100(%), f_(W)denotes a focal length of the overall zoom lens system at the time ofinfinite object point focusing at the wide angle end, IH_(W) denotes themaximum image height at the time of infinite object point focusing atthe wide angle end, and ω_(W) denotes a half angle of view at the timeof infinite object point focusing at the wide angle end.
 15. The zoomlens according to claim 1, wherein the second lens unit includes inorder from the object side to the image side, the object-side sub lensunit having a positive refractive power and the image-side sub lensunit, and the object-side sub lens unit in the second lens unit includesone lens component, and in the lens component, only the object-sidesurface and the image-side surface are in contact with air in theoptical path, and the following conditional expression (13) is satisfied−1.5<SF_(UN21)<0.5  (13) where,SF _(UN21)=(R _(UN21O) +R _(UN21I))/(R _(UN21O) −R _(UN21I)) R_(UN21O)denotes a paraxial radius of curvature of an object-side surface of theobject-side sub lens unit in the second lens unit, and R_(UN21I) denotesa paraxial radius of curvature of an image-side surface of theobject-side sub lens unit in the second lens unit.
 16. The zoom lensaccording to claim 1, wherein the following conditional expression (14)is satisfied0.38<Σ_(2G) /f _(W)<0.75  (14) where, Σ_(2G) denotes a thickness of thesecond lens unit on an optical axis, and f_(W) denotes a focal length ofthe overall zoom lens system at the time of infinite object pointfocusing at the wide angle end.
 17. The zoom lens according to claim 1,wherein the second lens unit includes in order from the object side tothe image side, the object-side sub lens unit having a positiverefractive power and the image-side sub lens unit, and the object-sidesub lens unit in the second lens unit includes one lens component, andin the lens component, only the object-side surface and the image-sidesurface are in contact with air in the optical path, and the image-sidesub lens unit in the second lens unit includes a lens surface having anegative refractive power, and a positive lens which is disposed on theimage side of the lens surface.
 18. The zoom lens according to claim 1,wherein the following conditional expression (8) is satisfied1.17<|f ₃ /f ₂|<1.95  (8) where, f₂ denotes a focal length of the secondlens unit, and f₃ denotes a focal length of the third lens unit.
 19. Thezoom lens according to claim 1, wherein the following conditionalexpression (15) is satisfied1.3<|f ₃ /IH _(MAX)<2.5  (15) where, f₃ denotes the focal length of thethird lens unit, and IH_(MAX) denotes the maximum image height, anddenotes the maximum value in a case in which, the maximum image heightchanges with zooming.
 20. The zoom lens according to claim 1, whereinthe third lens unit includes a lens having a specific gravity more than0.9 g/cm³ and smaller than 1.3 g/cm ³.
 21. The zoom lens according toclaim 1, wherein the second lens unit includes a negative lens and apositive lens that satisfies the following conditional expression (16).63<v_(p1)<96  (16) where, v_(p1) denotes Abbe's number for a d-line ofany of the positive lenses in the second lens unit.
 22. The zoom lensaccording to claim 1, wherein the first lens unit includes in order fromthe object side to the image side, an object-side sub lens unit and animage-side sub lens unit, and the object-side sub lens unit in the firstlens unit includes a first negative lens, and the image-side sub lensunit in the first lens unit includes a second negative lens and a firstpositive lens.
 23. The zoom lens according to claim 22, wherein thefollowing conditional expression (3) is satisfied−0.9<SF_(2N)<1.5  (3) where,SF _(2N)=(R _(2NO) +R _(2NI))/(R _(2NO) −R _(2NI)), R_(2NO) denotes aparaxial radius of curvature of an object-side surface of the secondnegative lens in the first lens unit, and R_(2NI) denotes a paraxialradius of curvature of an image-side surface of the second negative lensin the first lens unit.
 24. The zoom lens according to claim 1, whereinthe following conditional expression (17) is satisfied0.6<fb _(W) /IH _(MAX)<1.8  (17) where, fb_(W) denotes an air-convertedback-focus at the time of infinite object point focusing at the wideangle end, and IH_(MAX) denotes the maximum image height, and denotesthe maximum value in a case in which, the maximum image height changeswith zooming.
 25. The zoom lens according to claim 1, wherein thefollowing conditional expression (18) is satisfied0.4<f ₁ /f ₃<1.2  (18) where, f₁ denotes a focal length of the firstlens unit, and f₃ denotes a focal length of the third lens unit.
 26. Thezoom lens according to claim 1, wherein the following conditionalexpression (6′) is satisfied0.45<Σ_(2G) /f ₂<0.75  (6′) where, Σ_(2G) denotes a thickness on anoptical axis of the second lens unit, and f₂ denotes a focal length ofthe second lens unit.
 27. The zoom lens according to claim 1, whereinthe following conditional expression (7) is satisfied0.6<f _(UN21) /f ₂<1.8  (7) where, f_(UN21) denotes a focal length ofthe object-side sub lens unit in the second lens unit, f₂ denotes afocal length of the second lens unit.
 28. The zoom lens according toclaim 1, wherein the following conditional expression (19) is satisfied3<LTL _(W) /fb _(W)<13  (19) where, LTL_(W) denotes a sum of an overalllength of the zoom lens at the time of infinite object point focusing atthe wide angle end and an air-converted back focus, the overall lengthis a distance on an optical axis from a refracting surface of the zoomlens nearest to the object side and a refracting surface of the zoomlens nearest to the image side, and fb_(W) denotes the air-convertedback focus at LTL_(W).
 29. The zoom lens according to claim 1, whereinthe following conditional expression (20) is satisfied0.6<f _(UN21) /f _(W)<1.9  (20) where, f_(UN21) denotes a focal lengthof the object-side sub lens unit in the second lens unit, and f_(W)denotes a focal length of the overall zoom lens system at the time ofinfinite object point focusing at the wide angle end.
 30. The zoom lensaccording to claim 29, wherein the following conditional expression(20′) is satisfied0.6<f _(UN21) /f _(W)<1.6  (20′) where, f_(UN21) denotes the focallength of the object-side sub lens unit in the second lens unit, f_(W)denotes the focal length of the overall zoom lens system at the time ofinfinite object point focusing at the wide angle end.
 31. The zoom lensaccording to claim 1, wherein the following conditional expression (21)is satisfied0.35<ΔD ₁₂ /f _(T)<0.6  (21) where,D ₁₂ =D _(12W) −D _(12T), D_(12W) denotes the distance between the firstlens unit and the second lens unit at the wide angle end, D_(12T)denotes the distance between the first lens unit and the second lensunit at the telephoto end, both D_(W) and D_(12T) are distances on anoptical axis at the time of infinite object point focusing, and f_(T)denotes a focal length of the overall zoom lens system at the time ofinfinite object point focusing at the telephoto end.
 32. The zoom lensaccording to claim 1, wherein the following conditional expression (22)is satisfied0.35<|f ₃ /ER _(S)|<1.05  (22) where, f₃ denotes the focal length of thethird lens unit, and ER_(S) denotes the maximum radius of an opening ofthe aperture stop.
 33. The zoom lens according to claim 1, wherein thefirst lens unit includes a plastic aspherical lens which satisfied thefollowing conditional expression (23)0.0001<|ASP _(o)-ASP _(I) |/IH _(33W)<0.02  (23) where, IH_(33W) denotesa distance from an optical axis of a position at which, a principal rayintersects with a paraxial image plane such that, an incidence-side halfangle of view of the zoom lens at the time of infinite object pointfocusing at the wide angle end becomes 33°. ASP_(o) denotes an amount ofaspherical deviation at a position at which, a distance of anobject-side surface of the plastic aspherical lens from the optical axisbecomes IH_(33W), ASP_(I) denotes an amount of aspherical deviation at aposition at which, a distance of an image-side surface of the plasticaspherical lens from the optical axis becomes IH_(33W), and the amountof aspherical deviation is a distance in an optical axial direction,from a reference spherical surface for which, a vertex of a surfaceintended is let to be the vertex, and a radius of curvature is let to besame as a paraxial radius of curvature of the surface intended, up tothe surface intended, and a case in which, the intended surface is onthe image side with respect to the reference spherical surface is let tohave a positive sign.
 34. The zoom lens according to claim 33, whereinboth the object-side surface and the image-side surface of the plasticaspherical lens are aspheric surfaces.
 35. The zoom lens according toclaim 1, wherein at the wide angle end, a light ray of half angle ofview 33° or more is capable of passing through the zoom lens, and thefollowing conditional expression (24) is satisfied2.6<f _(T) /f _(W)<5.0  (24) where, f_(T) denotes a focal length of theoverall zoom lens system at the time of infinite object point focusingat the telephoto end, and f_(W) denotes a focal length of the overallzoom lens system at the time of infinite object point focusing at thewide angle end.
 36. The zoom lens according to claim 1, wherein thesecond lens unit includes a single lens having a positive refractivepower which is disposed nearest to the object side in the second lensunit, and a cemented lens of a negative lens and a positive lens inorder from the object side, and the aperture stop is positioned betweenthe single lens and the cemented lens in the second lens unit.
 37. Animage pickup apparatus comprising: a zoom lens; and an image pickupelement which has an image pickup surface, and which converts an imageformed on the image pickup surface by the zoom lens, to an electricsignal, wherein the zoom lens is the zoom lens according to claim 1.